Press releases

When A Star Sheds Its Shells

2022 November 10

The third brightest star in the constellation Columba (Gamma Columbae), about 900 light years from Earth kept a sectret – which has now been disclosed by Dr. Andreas Irrgang from the Dr. Karl Remeis Observatory in Bamberg in collaboration with Prof. Dr. Norbert Przybilla, a former Remeis astronomer, now at Innsbruck University. The team discovered that the star once formed the heart of a binary star system and lost its shell when it engulfed its companion.

Artist’s impression of a Gamma Col-like star. The superimposed collar represents the catalytic nuclear cycle (named after Carl-Friedrich Weizsäcker and noble prize winner Hans Bethe) that fuses four hydrogen nuclei into one helium nucleus releasing huge amounts of energy deep in the stellar interior.
Credit: Collage: Prof. Dr. Norbert Przybilla (Innsbruck): https://www.eso.org/public/images/eso2010a/ https://supernova.eso.org/exhibition/images/0418_cno-1080/)

Their findings were recently published in the renowned journal Nature Astronomy.

Since the late 1930s, it has been known that stars generate their enormous radiation energy through nuclear fusion of hydrogen into helium at temperatures of many millions of degrees Celsius deep inside the star. This fusion takes place in a cyclic process in which carbon, nitrogen and oxygen act as catalysts. This results in a characteristic enrichment of nitrogen in the core of the star.

Because massive stars such as Gamma Col are wasteful with their nuclear energy supply, they only exist for a few million years before they pass away in a gigantic explosion, a supernova. This nuclear evolution is usually not directly observable because the very dense stellar envelopes shield the hot central fusion reactor. Predictions of stellar evolution models can therefore only be tested by observations of stellar surfaces of numerous stars.

For many years, Irrgang Przybilla have been observing massive stars by analysing their spectra using sophisticated model atmospheres. Now they made a unique discovery: the massive star Gamma Columbae in the southern constellation Columba showed anomalies in the chemical composition of its surface – deviating from what is expected for stars with similar mass.

Together with Prof. Dr. Georges Meynet, a leading stellar evolution theorist from the University of Geneva, they found the explanation.

Gamma Columbae once belonged to a binary system and orbited with another star around a common centre of mass and lost its envelope when it engulfed its companion star.

If the two stars were close together, the gravitational wave radiation caused the stellar orbits to shrink. When the stars were close enough to interact, a common envelope around both stars formed and was finally ejected. In this way the stellar core, the heart of the star, so to speak, was exposed. This suggests that Gamma Columbae may be the exposed core of what was originally a much more massive star in a former binary system.

Based on the composition found, the star formed with a mass of 12 solar masses and lost no less than 7 solar masses. It can be assumed that Gamma Columbae has reached about 90 per cent of its estimated lifetime of a good ten million years. This means that it should have less than two million years to live before it explodes.
Gamma Columbae offers even more: It shows complex light variations (“Pulsations”) caused by waves propagating through its envelope. Like earthquake waves are used to probe the interior of the Earth, the pulsations allow the deeper layers of Gamma Columbae to be probed. Futher observations of these pulsations will give insight into the past and future of binary stars in detail.

Original publication: doi.org/10.1038/s41550-022-01809-6

Andreas Irrgang
Andreas.Irrgang@sternwarte.uni-erlangen.de
+49 951 95222 16

Related press releases:

Swiss National foundation on idw:
https://idw-online.de/de/news803874
University of Geneva:
https://www.unige.ch/communication/communiques/en/2022/histoire-dun-strip-tease-cosmique

Astronomical Plate Archive: Ready for Science in the Virtual Obsevatory

2022 July 6

German observatories host a heritage of astronomical observations stored on historical photographic plates that show the starry sky (see Fig. 1). Together with the Leibniz Institute for Astrophysics Potsdam and the Universities of Hamburg and Tartu (Estonia), scientists at the Dr. Remeis-Sternwarte have digitised the astronomical images and published them online – after ten years, the project has now been successfully completed thanks to the financial support of the German Research Foundation (DFG).

Even though the oldest images are “only” 129 years old – a truly tiny moment compared to the standards otherwise applied in astronomy – they hold scientific treasures. For it is only with such images that today’s astronomers can study how their brightness changes over several decades at once. In this way, new research questions can be answered and millions and millions of stars can be observed more precisely and objectively.

In several steps since 2012, the research team has digitised the photographs from the archives of the partner institutes from the years 1893 to 1998 in the APPLAUSE database – short for Archives of Photographic Plates for Astronomical USE – and recorded them in a catalogue with details about the photograph, such as date, celestial section and location. In addition, the research network developed software that uses artificial intelligence to eliminate artefacts on the plates such as scratches or dust and to calibrate the images for quantitative research. Scientists worldwide now have 4.5 billion measurements of light sources at their disposal for their research.

Figure 1: Area of sky in the southern constellation Chamaeleon from the Bamberg Southern station at Mount John Observatory (New Zealand). Copyright. Dr. Remeis-Sternwarte

A total of over 94,000 photographic plates digitised

A significant proportion of the total of 94,090 photographic plates recorded are the approximately 40,000 photographs taken by the Dr. Karl-Remeis Observatory Bamberg. This is because they include photographs taken by Franconian researchers at observatories in the southern hemisphere between 1963 and 1976. These monitored the southern sky – unique
worldwide, as no other astronomical project surveyed it during this period. In addition, the research network developed software that uses artificial intelligence to eliminate errors on the plates such as scratches or dust and to calibrate the images, making them scientifically comparable. Scientists worldwide now have 4.5 billion measurements of celestial light sources at their disposal for their research.

But that’s not all: thanks to a scientific conference in Bamberg, other observatories became aware of the project. For example, the Thüringer Landessternwarte Tautenburg. It hosts the archive of the Karl Schwarzschild Observatory – the former observatory of the Academy of Sciences of the GDR – from the years 1960 to 1998 and made it available to the research network. Or the astronomical observatory of the Vatican State in Castel Gandolfo, whose scientists also came forward to have their archives entered into the database and thus opened it up to the worldwide research community.

New insights thanks to long-term sky patrol

Figure 2: Light curve of the X-ray binary HD49798 from the APPLAUSE data base (Copyright: Dr. Veronika Schaffenroth (Uni Potsdam)

But what insights can still be gained from the historical photographic plates today? With its surveys of the northern and southern skies in the last century, the Bamberg observatory aimed to examine stars whose brightness varies with time. For some objects, their physical composition is not known, i.e. exactly which gases they are made of. The star “HD49798” is a particularly interesting example. Its unsteady light variations were recorded on the Bamberg photographic plates in the 1960s and early 1970s, but could only be evaluated just now. They show that the star brightened in 1964/65 and then dimmed again until 1974 (see Fig. 2). In addition, there were rapid changes in light within a few days. In 1999, satellite measurements finally revealed that the star was emitting X-rays. Today, the assumption is that it comes from an invisible, very compact companion, possibly a neutron star. The long-term variations in brightness were previously unknown because no sequence of measurements existed over such a long period – ten years. The historical data from the photographic plates therefore provide important clues for astronomy, which will have to be evaluated by researchers in the coming years. Actually, the star duo is still unique, because no other constellation of this type has been observed so far.

Access to the published data:

https://www.plate-archive.org/

See also:

https://idw-online.de/de/news797759

https://www.uni-hamburg.de/newsroom/presse/2022/pm38.html

https://www.aip.de/de/news/digitization-project-photographic-plates-completed/

For more information contact:

Ulrich Heber
Ulrich.Heber@sternwarte.uni-erlangen.de
+49 951 95222 14

Tracking superbubbles and supergiant shells in the Magellanic Clouds

2021 August 27

Our PhD-student Caroline Collischon published a paper titled “Tracking down the origin of superbubbles and supergiant shells in the Magellanic Clouds with Minkowski tensor analysis”. In collaboration with Prof. Dr. Klaus Mecke of the Institute of Theoretical Physics, an automatic bubble-recognition routine based on Minkowski functionals (MF) and tensors (MT) was developed to detect bubble-like interstellar structures in optical emission line images.
Such interstellar bubbles are created by strong stellar winds of massive stars and their supernova explosions. In the optical images, one can see the emission from the shells consisting of swept-up interstellar gas. In this project, the interstellar medium in the Magellanic Clouds, which are the largest satellite galaxies of our Milky Way, was studied.
Bubbles are detected by tracing back the origins of filaments by drawing lines perpendicular to each filament. For a circular bubble, those lines meet in the center and a large line density is generated. This allows for an automatic bubble detection.

H alpha image with detected bubbles. Lines are drawn perpendicular to filaments and high line density marks the centers of bubbles.

In line-density maps of the Large Magellanic Cloud (LMC), maxima can be found in regions with high star formation in the past, often inside supergiant shells (SGS). In the Small Magellanic Cloud (SMC), bubble detection is impaired by the more complex projected structure of the galaxy. Line maps at large scales show large filaments in the SMC in a north-south direction, especially in the [SII] image. The origin of these filaments is unknown and requires further investigation.

Further information:

Publication in A&A

For more information contact:

Caroline Collischon
caroline.collischon@fau.de
+49 951 95222 16

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Klaus Mecke

A teardrop as a supernova progenitor

2021 July 13

Supernovae type Ia are very important standard candles for distances in the universe, as they are very bright. Since the mechanism will produce an explosion of a certain luminosity the brightness of the event observed from earth will immediately give a glimpse at the distance of the supernova. In order to understand these processes in the universe it is crucial to know which systems can end in a supernova of this type. In order to explain the type Ia two scenarios can be used, both requiring at least a binary system. In all cases a white dwarf, the end-state of a low mass star, will somehow exceed the so called Chandrasekhar limit of 1.4 solar masses and as a result of that a thermonuclear explosion is triggered. The first mechanism is that a white dwarf accretes matter from its companion star, hence at some point exceeding the mass limit. Another option, however, is the merger of a white dwarf and a compact companion star. Finding progenitors of such systems is crucial to understand under which circumstances these supernovae occur. Nevertheless, it is very hard to find such systems, with only a few known so far.

Prof. Dr. Ulrich Heber, Dr. Andreas Irrgang, and PhD-student David Schneider from the Remeis observatory are part of an international team of scientists who found a new progenitor system located 1,500 lightyears away from earth. The binary system HD 265435 consists of a hot subdwarf star, a stripped helium core burning star, and a white dwarf. The stars were analyzed using spectra, which were also taken with the ESI spectrograph at Keck observatory, light curves from TESS, and astrometric data from the Gaia space mission. The results show that the binary system consist of a pulsating subdwarf OB star and a white dwarf with a carbon-oxygen core which orbit each other with a period shorter than 100 minuets. Due to gravity of the white dwarf the subdwarf star is distorted and has a teardrop-like form (see image). The entire system has a mass of about 1.65 solar masses, therefore, exceeding the Chandrasekhar mass.

Artist’s impression of the HD265435 system at around 30 million years from now, with the smaller white dwarf distorting the hot subdwarf into a distinct ‘teardrop’ shape. Credit: University of Warwick/Mark Garlick

Simulations show that both components of the system will form a supernova type Ia in approximately 70 Million years. Most likely the subdwarf will become a white dwarf itself in the future. While orbiting each other the orbit will get tighter due to radiation of gravitational waves. Finally both white dwarfs will merge, resulting in a supernova of type Ia. However, depending on the properties of the subdwarf, it could also be possible that the white dwarf accretes enough mass from its companion before a merging event. Therefore, both proposed scenarios for type Ia supernovae could occur in the system HD 265435.

Such systems are very rare. Actually, even with this new discovery too few systems are known in our Galaxy to explain the observed rate of occurance of Ia supernovae in other galaxies. Future missions such as the Vera Rubin telescope will have to find the hidden population of supernova Ia progenitors.

Further information:

For more information contact:

Ulrich Heber
Ulrich.Heber@sternwarte.uni-erlangen.de
+49 951 95222 14

Andreas Irrgang
Andreas.Irrgang@sternwarte.uni-erlangen.de
+49 951 95222 16

eROSITA EDR

2021 June 25

Nearly two years after launch, the eROSITA consortium, in which the observatory is heavily involved, will have its first data release. This release, called early data release (EDR), will include the calibration and science verification observations. These observations were carried out between September and December 2019 before eROSITA started its planned all-sky survey. The EDR includes about 100 single observations of multiple sky regions. Many different astrophysical objects have been observed during this phase, covering objects within the Milky Way up to distant galaxy clusters. Those data, which can be used for images, spectra and time-domain analysis, will help scientists around the world to gain a better understanding of the X-ray sky. From now on the data is public and can be used.

The EDR is accompanied by the release of 35 papers, in which these data have been studied by scientists of the eROSITA consortium. Within the consortium, students and professors alike have put great effort into the publications and the EDR itself. About 40% of all EDR publications are led by female scientists. Two of these scientist are from the Remeis observatory, Dr. Sara Saeedi and Prof. Dr. Manami Sasaki.

While most papers deal with the data from the “eROSITA final equatorial depth survey” ( eFEDS), other commissioning and calibration data are analyzed in the papers as well. For its first-light observation eROSITA observed the Large Magellanic cloud (LMC), the closest and largest satellite galaxy of the Milky Way. Its first light image is shown in the picture. The analysis of the LMC EDR data was led by Prof. Manami Sasaki and involved colleagues from the observatory and from around the world. In her publication, the distribution of hot plasma within the LMC was analyzed, which revealed complex structures in the interstellar medium.

Mosaic of the EDR observation of the LMC. On the left side the Tarantula-nebula and several supernova remnants can be seen. The image also shows the diffuse emission in the LMC. © eROSITA collaboration, Sasaki et al.

Five eROSITA calibration observations have targeted the massive globular cluster (GC) 47 Tuc in the Galactic halo. Previous radio/X-ray observations, which were limited to the center of 47 Tuc, confirmed the presence of 23 millisecond pulsar within the half mass radius of this GC. For the first time observations of eROSITA gave the opportunity to intensively study the X-ray sources in 47 Tuc. The study reveals the presence and also the nature of low luminosity X-ray sources, which are mainly different types of accreting white dwarfs, and low mass X-ray binaries in this GC.

Multiple junior and senior scientists from the observatory were involved in the work presented in the 35 papers. The EDR will help scientist to prepare for the upcoming eROSITA all-sky scans and gives an already impressive insight into the capabilities of eROSITA.

Further information:

For more information contact:

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Sara Saeedi
sara.saeedi@fau.de
+49 951 95222 24

Jörn Wilms
Joern.Wilms@sternwarte.uni-erlangen.de
+49 951 95222 13

Colliding clouds in the LMC

2021 April 19

The large Magellanic Cloud (LMC) is the largest satellite galaxy of the Milky Way. The LMC is home to many interesting objects such as SN1987A or the nebula 30 Doradus. Also known as the Tarantula nebula, 30 Doradus is an emission nebula and one of the largest and most active star forming regions in the Local Group. The nebula is heated by its young and massive stars.

When looking at the surrounding region of 30 Doradus in the X-ray regime a large structure called the X-ray spur can be seen. This triangular shaped structure is about 1 kpc in size and located to the south of 30 Doradus. The emission from this spur is more energetic than from the surrounding interstellar medium (ISM), therefore indicating that the plasma inside the spur region is hotter than expected from the ambient ISM.

The spur was first discovered in the 1990s by the german ROSAT X-ray mission. Now Scientists from the Dr. Karl Remeis-Observatory studied the X-ray spur using ESAs XMM Newton Observatory. The analysis shows that the temperature of the plasma within the spur is indeed higher and is quite similar to the temperatures observed in 30 Doradus.

In order to find the reason as to why the plasma is heated multiwavelength data was analyzed. As no evidence for young massive stars was found, they can be excluded as possible heating mechanism. However, the analysis revealed that the spur is in fact located between two giant clouds made up of atomic hydrogen. These clouds are colliding with each other, which also explains the heating of the region. The collision itself seems to have started at the position of 30 Doradus and has spread further down south, therefore connecting the X-ray spur with 30 Doradus.

The two cold atomic hydrogen components are shown in red and green. The hot plasma is blue. © Jonathan Knies

The X-ray spur region is shown in the image. The two clouds, which were observed with radio telescopes, are displayed in red and green, while the XMM data, here shown in blue, clearly shows the region where the clouds are colliding. The contours in cyan and magenta trace carbon-monoxide and H-alpha emission, respectively, which are both indicators for new star forming regions. Therefore, it can be expected that the spur will evolve into a new star formation region very similar to 30 Doradus.

Further information:

FAU press release (EN)
ESA press release (EN)
publication in A&A: here

For more information contact:

Jonathan Knies
Jonathan.Knies@fau.de
+49 951 95222 12

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Black hole mass in Cygnus X-1 higher than previously thought

2021 February 19

The first black hole ever discovered in our Galaxy is part of the high-mass X-ray binary Cygnus X-1. This system consist of two components, the blue giant star HD 226868 and a black hole. Previously, the distance was thought to be around 6100 lightyears, which indicated that the black hole has a mass of around 14 solar masses.

However, a new distance measurement published this week in Science, suggests that the distance to Cygnus X-1 actually is higher than previously thought. Scientists from the Remeis-Oberservatory were involved in this new discovery as well. Using the Very Long Baseline Array, a group of radio telescopes spread across the US, the parallax of the binary system was measured. Due to the Earths movement around the sun, nearby stars seem to move compared to distant galaxies. This movement is called the parallax, with more distant objects showing smaller movements. Using this method, the distance to Cygnus X-1 was now determined to be 7200 lightyears. This has implications on the masses of the components of the system, which are in fact higher than previously assumed.

Artist’s impression of the X-ray binary Cygnus X-1. The black hole can be seen on the left and the blue giant companion on the right. The sun is shown for comparison. © International Centre for Radio Astronomy Research

The new distance suggests a black hole mass of about 20 solar masses, which makes Cygnus X-1 the most massive black hole known to exist in an X-ray binary.
This exciting discovery gives new insight into the formation of black holes. Stellar mass black holes are produced by the death of a massive star, called Supernova. The massive progenitor stars are thought to lose a lot of mass throughout their life time due to strong stellar winds. However, in order to produce a black hole as it exists in this system, the winds had to be weaker than assumed and the progenitor star must have had a mass of ~60 solar masses.

Further information:

FAU press release (DE)
Original publication in Science: Cygnus X-1 contains a 21–solar mass black hole—Implications for massive star winds
Youtube: CYGNUS X-1: the most massive black hole near to Earth

For more information contact:

Jörn Wilms
Joern.Wilms@sternwarte.uni-erlangen.de
+49 951 95222 13

Detection of large-scale eROSITA bubbles in the halo of the Milky way

2020 December 11

The eROSITA bubbles. The false-colour map shows extended emission at energies of 0.6-1.0 keV. The contribution of the point sources was removed and the scaling adjusted to enhance large-scale structures in our Galaxy. © MPE/IKI

Schematic view of the eROSITA (yellow) and Fermi bubbles (purple). The galactic disk is indicated with its spiral arms and the location of the Solar System is marked. The bubble structures are comparable in size to the whole galaxy. © MPE

The first all-sky survey by the eROSITA X-ray telescope revealed the entire X-ray Universe with unprecedented detail in June 2020. The study of one particularly interesting feature, the large-scale “eROSITA bubbles” in the halo of the Milky Way, has now been published in Nature.

What has been named “eROSITA bubbles” are large-scale structures in the shape of an hourglass that seem to be centered on the center of our galaxy and the show a striking similarity to the Fermi bubbles, which have been detected about a decade ago at gamma-ray energies. The bubbles in the X-rays are highlighted in the false-color map on the right, which shows extended emission at energies from 0.6 to 1 keV. These structures are produced by shocks in the hot gas envelope of our galaxy, which most likely have been produced by a massive energy output from the central Galactic region.

In comparison to the Fermi bubbles, the “eROSITA bubbles” are even larger and extend over a distance equal to the size of our galaxy (see the Schematic view on the right). The large-scale disturbances in the hot gas envelope could have been caused either by a burst of star formation or an outburst from Srg A*, the central supermassive black hole in the Galactic Centre.

Although the black hole is dormant now, it might have been active in the past. The energy needed to power the formation of the bubbles is estimated to be equivalent to the energy released by 100,000 supernovae, which is similar to the power output of active galactic nuclei.

Further information

FAU press release (DE/EN)
MPE press release (DE/EN)
Original publication in Nature: Detection of large-scale X-ray bubbles in the Milky Way halo

For more information about eROSITA and the X-ray sky, please contact:

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Jörn Wilms
Joern.Wilms@sternwarte.uni-erlangen.de
+49 951 95222 13

Humbold Fellow Javier García receives 2021 Early Career Award

2020 October 14

Courtesy of J. García

Javier García, who has been a Humboldt Fellow at our observatory since 2017, has been awarded the ‘2021 Early Career Award’ by the American Astronomical Society. His main focus is to understand the X-ray radiation around accreting compact objects, such as black holes and neutron stars. With his state-of-the-art model he combines relativistic reflection and the ionization structure of hot accretions disks, which can be observed with X-ray satellites.
The award acknowledges his significant contributions to his working field, which is an intersection of computational atomic physics and high-energy spectral modelling, within only 10 years of receiving his PhD.

The whole observatory congratulates Dr. García on this honorable award.

Mysterious binary star system in space

2020 September 17

The researchers observed the system simultaneously with two X-ray satellites. (Illustration: Victoria Grinberg)

Binary stars are well known to astrophysicists. One stellar double-act in particular has drawn their attention, as part of the X-ray radiation that binary star systems usually emit is missing, and the x-rays it did emit seemed to have strange properties. A research team led by FAU observed a binary star system using X-ray satellites to find some answers. Their results were published in the journal ‘Astronomy and Astrophysics’.

Binary star systems are not unusual in space. Even if like IGR J16318-4848, located in one of the spiral arms of our galaxy, one of the partners consists of a neutron star, the ultra-compacted remains of a stellar corpse. Its partner appears to be similarly exotic – a supergiant star that is several times the mass of our sun. On top of that, this monstrous cosmic litterbug blasts out vast amounts of iron into space. ‘Usually, we can detect a broad spectrum of soft and hard X-rays from such systems,’ explains Prof. Dr. Jörn Wilms from the Astronomical Institute of FAU in the Dr. Karl Remeis Observatory in Bamberg. But this system proved a tough nut to crack for astrophysicists not only because the entire soft X-ray radiation was missing but also because the hard X-rays have very surprising properties. Jörn Wilms, his doctoral candidate Ralf Ballhausen and a research team from Germany, the Netherlands, Spain and the USA were only able to solve this problem with the help of two X-ray satellites and computer models, which they used to simulate this mysterious binary system.

Further information

Full FAU press release (also available in German)
NuSTAR press release
Original publication: Dust and gas absorption in the high mass X-ray binary IGR J16318−4848

For further information please contact:

Ralf Ballhausen
Ralf.Ballhausen@sternwarte.uni-erlangen.de
+49 951 95222 44

Jörn Wilms
Joern.Wilms@sternwarte.uni-erlangen.de
+49 951 95222 13

Deepest image of the X-ray sky

2020 June 19

The eROSITA telescope has finished its first sweep across the sky and presents us the deepest image of the X-ray that humanity has ever seen. This map is about 4 times deeper than what has been seen by the ROSAT all-sky survey 30 years ago and contains over 1 million hot objects, like binaries, supernova remnants and active galaxies. Over the next 3.5 years, eROSITA will continue surveying the sky and create such an all-sky image every half year. The final map, with all individual images combined, will have an even higher sensitivity, which will used by astrophysicists and cosmologists in the next decades to unveil the hot and energetic universe.

The X-ray sky seen through eROSITA eyes from 0.3 to 2.3 keV. © Jeremy Sanders, Hermann Brunner and the eSASS team (MPE); Eugene Churazov, Marat Gilfanov (on behalf of IKI)

The Carina nebula and its stellar environment (red: 0.2-0.5 keV, green: 0.5-1.0 keV, blue: 1.0-2.0 keV). © Manami Sasaki (Dr. Karl Remeis Observatory/FAU), Davide Mella

The Dr. Karl Remeis observatory is a part of the Collaboration and works on both extragalactic and galactic X-ray sources, like the Carina nebula.
The Carina nebula is one of the largest diffuse nebulae in the Milky Way and hosts a large number of massive, young stars. The brightest of these stars (also in X-rays) is Eta Carinae.

For the full press release, check out the MPE Press Releases.

For more information about eROSITA and the X-ray sky, please contact:

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Jörn Wilms
Joern.Wilms@sternwarte.uni-erlangen.de
+49 951 95222 13

2020 Dissertation Prize

2020 February 28

The Laboratory Astrophysics Division (LAD) of the American Astronomical Society (AAS) announced Dr. Natalie Hell, a former PhD student at the Dr. Karl Remeis-Observatory, to receive its 2020 Dissertation Prize. Natalie got this prize because of her thesis “Benchmarking Transition Energies and Emission Strengths for X-ray Astrophysics with Measurements at the Livermore EBITs”. She is being cited “for groundbreaking laboratory measurements necessary for accurate, reliable interpretation of high-resolution X-ray spectra from astronomical sources.” We warmly congratulate Natalie for her amazing work. For more information please visit the LAD webpage.

A special place

2020 January 17

Without a doubt the Dr. Karl Remeis-Sternwarte is a special place of the FAU. In the series “Besondere Orte der FAU” the university of Erlangen-Nuremberg presents its Astronomical Institute located in Bamberg.

A stripped helium star in the potential black hole binary LB-1

2020 January 10

The publication of Chinese astronomers about a black hole as massive as 70 solar masses immediately triggered theoretical investigations as well as additional observations by other astrophysicists, because theoretically stellar black holes have masses of about ten times that of our Sun. The Astronomical Institute of the Friedrich-Alexander-Universität Erlangen-Nürnberg together with astronomers of the University of Potsdam had a closer look at this mystical object. Today, they published a paper describing that it may not necessarily be a black hole, it could possibly be a massive neutron star or even an ‘ordinary’ star. See also the press release at the ECAP webpage.

First light of eROSITA

2019 October 22

On 22 October 2019, the first-light images of the eROSITA telescope taken with all seven X-ray telescope modules were presented to the public. The first combined X-ray images show our neighboring galaxy, the Large Magellanic Cloud (shown in figure), and a pair of interacting clusters of galaxies at a distance of about 800 Million lightyears. These images show remarkable details and demonstrate the promise of the ambitious science program planned with the space-borne telescope. Scientists from the Remeis-Observatory have been involved in simulations and are responsible for near-real time analysis and science data analysis. Everyone at the observatory is looking forward to the upcoming scientific results.

The LMC as seen by eROSITA. A few interesting objects such as the Tarantula nebula or the Supernova 1987A have been marked in this image. (Credit: F.Haberl, M. Freyberg and C. Maitra, MPE/IKI)

Runaway stars and black holes

2019 September 24

Led by astronomers from FAU, an international consortium has recently discovered a new high-velocity star (HVS). These are stars which move at great speed through the Milky Way, sometimes travelling so fast that they may eventually leave our galaxy. Until now, scientists have not yet been entirely sure where these runaway stars find the enormous impulse they need to be able to accelerate to such high speeds. Together with their colleagues, Dr. Andreas Irrgang and Prof. Dr. Ulrich Heber from the Dr. Karl Remeis observatory in Bamberg, the Astronomical Institute of FAU, have collected data which could give new insights into the origin of HVS using one of the largest telescopes in the world, the Keck Observatory in Hawaii.

Astronomers try to find out why runaway stars leave their birth cluster in a galaxy. Mid-size black holes may be responsible. (Image: FAU/Andreas Irrgang)

Using the data, the researchers traced the trajectory of a newly discovered runaway star and discovered that the standard ejection mechanisms could not apply to this star. The researchers were able to rule out the standard scenario, in other words interaction with the supermassive black hole at the centre of our universe. Instead, they suggest that an intermediate-mass black hole may be responsible. Black holes such as this have not yet been found. Based on the traced trajectory of the new HVS, however, astronomers now have an idea where they could look for possible mid-size black holes.

For further information please contact:

Andreas Irrgang
Andreas.Irrgang@sternwarte.uni-erlangen.de
+49 951 95222 16

eROSITA on its way to L2

2019 July 13

On 13 July 2019, a proton-M rocket successfully launched the
Spectrum-X-Gamma satellite with the German eROSITA instrument. As of
17:00 CEST, the systems on Spectrum-X-Gamma appear to be nominal and the
temperatures of the eROSITA instrument are also in the nominal range.

Zombie stars on the run

2019 July 5

An international consortium led by FAU astronomers discovered three hyper-velocity stars (HVS), which survived supernova explosions. These “Zombie” stars could give clues concerning how the chemical elements are created and distributed in the Universe. Not only a new class of HVS has been discovered, but also a new physical slingshot mechanism to eject the stars has been uncovered.

Artists impression of the Gaia satellite measuring the stars of the Milky Way. (c/o: ESA/ATG medialab/ESO/S. Brunier)

First discovered in 2005, hyper-velocity stars move through space at such a high speed that they will escape from the Galaxy. Despite an intense search no more than two dozen HVS have been discovered up to now. How these stars gain their enormous momentum to overcome the gravitational attraction of the Galaxy is still under discussion. “The most popular explanation is, that the monster black hole in the centre of the Milky Way disrupts a binary star that comes too close”, Prof. Dr. Ulrich Heber from FAU’s astronomical institute, one of the discoverers of the first HVSs, says. “More recent investigations, however, have shown that there have to be alternative slingshot mechanisms to explain the diversity of HVSs.” his FAU colleague, Dr. Andreas Irrgang, adds.

A new class of star discovered

The Gaia space observatory of the European Space Agency (ESA) has paved the way to understand the origin of HVS. Gaia’s astrometric data, published in April 2018, allowed for the first time the three dimensional trajectories of HVS through the Milky Way to be calculated and the place of origin to be identified. FAU astronomer, Dr Roberto Raddi, cross-matched the Gaia data with other astronomical catalogs to search for new HVSs and made an astonishing discovery: two new HVS that are strikingly similar to the exotic HVS, LP 40-365, netted serendipitously two years before by another team. An international collaboration consisting of astronomers from ten universities, in Germany, the UK, USA, and Italy carried out an extensive observational campaign with large telescopes, including the Hubble Space Telescope and the European Very Large Telescope: A new class of star was found.

The chemical composition is unique

The most important result was the uniquely peculiar composition of the new stars. They consist mostly of neon and oxygen. No trace of hydrogen and helium were detected, which are the dominant constituents of normal stars like the Sun. How is this possible? “Explosive thermonuclear explosions, such as in a hydrogen-bomb, may transform light chemical elements into heavier ones by nuclear fusion.” Dr Roberto Raddi explains. “Indeed, this has been proven to happen in thermonuclear supernovae caused by the explosion of a so-called white dwarf, an Earth-sized degenerate star. A white dwarf may explode if it accretes matter from a companion star”, he adds.

Zombie stars survived Supernovae

Two hyper-velocity star ejected in a supernova explosion.

Did FAU astronomers detect zombie-dwarfs, survivors of supernovae? Previous numerical simulations suggested that such an explosion would destroy the white dwarf completely. The former companion would be left behind and then ejected at hyper-speed. New models, however, revealed that in specific conditions the white dwarf is not entirely disrupted. About 20% of the mass may remain and form this exotic type of object, which is predicted to consist of neon, oxygen, magnesium, aluminum, and heavier elements, like manganese, iron, and nickel.
The observed abundances of these chemical elements of the new class of star are exactly what is predicted by the numerical simulations. But it remained unclear, why these relics of a stellar death contain no carbon, which they should have according to the numerical models. “This is one of the open questions, still to be answered”, Roberto Raddi says.

Supernova explosion create a HVS pair

How is the white dwarf relic ejected – and what will happen to the companion star? The researchers came up with a plausible explanation. The stellar companion had to be very close to the white dwarf for mass to be transfer to the latter, which required both stars to orbit their common centre of mass at extreme velocities. When the white dwarf exploded, it received a kick so strong to unbind the binary, causing both partners to fly out in different direction at hyper-speed. “Actually, two hyper-velocity stars were launched at the same time.” Ulrich Heber concluded. “Unfortunately, it will be very difficult to find the former companion star to any of the zombie dwarfs, because according to our estimates the ejection happened already 40 million years ago.”
The team succeeded to discover a new class of HVS as well as to uncover a new physical slingshot mechanism for HVS.
The results are accepted for publication in the renowned scientific journal Monthly Notices of the Royal Astronomical Society (https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stz1618/5521904 or https://arxiv.org/pdf/1902.05061.pdf)
The journal Nature reported the paper as a research highlight:
https://www.nature.com/articles/d41586-019-02083-9

Additionally, an article about the results is also published at SPIEGEL Online: https://www.spiegel.de/wissenschaft/weltall/forscher-entdecken-zombie-sterne-in-der-milchstrasse-a-1276102.html

For further information please contact:

Roberto Raddi
roberto.raddi@fau.de
+49 951 95222 16

Ulrich Heber
Ulrich.Heber@sternwarte.uni-erlangen.de
+49 951 95222 14

Spektr-RG paper model (eROSITA, ART-XC)

2019 July 1

Are you prepared for the launch of eROSITA in July 2019? We are glad to provide you the Spektr-RG paper model. This model is in the scale of 1/48 and shows great detail of the eROSITA and the ART-XC X-ray telescopes. This paper model kit provides you with all parts to build up your own X-ray observatory and you can download it right here. A special thanks goes to Thorsten Brand who created this nice model.

Software and Data Analysis for eROSITA at the Remeis-Observatory

2019 June 17

The eROSITA X-ray telescope on the SRG satellite. Credit: Roscosmos / DLR / Lavochkin / SRG / Anatoly Zak / RussianSpaceWeb

On Friday June 21st 2019 a proton M rocket will be launched at Baikonur, on board the SRG satellite. Part of this satellite is the eROSITA X-ray telescope developed by German an Russian scientists. The Astronomical Institute of the FAU Erlangen-Nuremberg is greatly involved in the development of the software used for the telescope and future data analysis. We are looking forward to the launch and scientific output. For more information see
FAU News Page and ECAP News Page.
Stay tuned for social media coverage on our Twitter and Instagram accounts.

Large Surveys with small telescopes: Past, present, and future – A scientific conference held in Bamberg from March 10 to 13, 2019

2019 April 16

In the context of the digitisation project of astronomical plates funded by the Deutsche Forschungsgemeinschaft (DFG) entitled “Digitalisierung astronomischer Fotoplatten und ihre Integration in das internationale Virtual Observatory”, a consortium of astronomers from the Hamburger Sternwarte, the Leibniz Institut für Astrophsik and the Dr. Remeis-Sternwarte in Bamberg organized a scientific conference entitled Large Surveys with small telescopes: Past, present, and future.

Participants from the Large Surveys with small telescopes Conference

About seventy astronomers from 16 countries around the globe met at the premises of the University of Bamberg to disclose synergies of historic astronomical observations stored on photographic plates with modern digital Sky surveys.

Large wide-field surveys have been carried out since more than a century, starting with the Carte du Ciel in the late nineteenth century and have been recorded on photographic plates. With the advent of CCD detectors monitoring the Sky became even more intense. Wide field surveys are carried out with small telescopes and cameras. Already with the Henry Draper Memorial project, spectroscopy became an important scientific technique for such surveys, early-on with objective prisms and latterly with multi-fiber instruments . Most of the ongoing surveys are dedicated to specific scientific aims, such as search for MACHOS, exoplanet transits or nearby asteroids, but provide data sets for a wide range of astrophysics research, such as binary light curves, stellar pulsations, and eruptions to name a few. Many future surveys will also be based on small telescopes, both on ground and in space.

The information stored in photographic plates distributed around the globe became accessible only recently, by digitization, calibration and integration into data bases such as DASCH or APPLAUSE.

Because a huge amount of data is piling up in the data bases of the different projects an important task is to combine the information and harvest it in an optimum way. To this end, the meeting aims to bring together researchers working on the photographic heritage, with those involved in ongoing and future digital surveys. Combing data sets requires in depth knowledge of calibration. Studying the objects requires the sophisticated tools of astroinformatics (big data, deep learning), which shall be addressed in the conference’ program.

The programme covered the following topics:

Past: History, plate archives, spectroscopy, digitization, calibration, catalogs, data bases, VO integration, linkage to modern digital surveys
Present: Digital surveys: Telescope (networks), robotic telescopes, photometry, astrometry, spectroscopy, catalogs, reduction and calibration pipelines, data base access, and VO integration.
Future: Ground based optical surveys with small telescopes under developement. Link to space-based surveys, astroinformatics, big data, and machine learning

Proceedings:

The presentations are available through: https://www.plate-archive.org/applause/project/lswst/

The nature of very high energy gamma-rays from superbubbles revealed

2019 January 24

An international scientific team, including Prof. Dr. Manami Sasaki from Dr. Karl Remeis Observatory, Bamberg, and the Erlangen Centre for Astroparticle Physics has used NASA’s Chandra X-ray Observatory – one of the most sophisticated X-ray observatories built to date – to reveal how very high energy (VHE) gamma-rays are produced by cosmic rays accelerated inside the 30 Doradus C superbubble, the only known VHE gamma-ray superbubble. The results of the work have been published in Astronomy and Astrophysics.

Chandra X-ray Observatory image of the 30 Doradus C revealing its X-ray shell in unprecedented detail. Chandra stared at 30 Doradus C for nearly a day to gather the data necessary to produce this image.

30 Doradus C is located in the Large Magellanic Cloud (LMC), a dwarf satellite galaxy of the Milky Way at a distance of about 170,000 light years. Even at this great distance it is visible to the naked eye in the southern hemisphere. Star formation is proceeding at a high rate in the LMC and very high mass stars (many tens the mass of the sun) are being born into new, massive stellar clusters. Collectively, through their powerful stellar winds and later their supernova remnants, these massive stellar populations blow huge ‘superbubbles’ into the surrounding interstellar medium. It is at the blast wave of the interior supernova remnants that cosmic rays are thought to be accelerated.

VHE gamma-rays are excellent tracers of cosmic ray accelerators such as supernova remnants. Charged particles are accelerated to incredibly high velocities and VHE gamma-rays can be produced either by accelerated electrons interacting with light, or accelerated protons interacting with gas. While VHE gamma-rays have been detected from 30 Doradus C before, it is not clear which mechanism dominates the gamma-ray production.

A key piece of evidence to address this question is the strength of the magnetic field near the acceleration site. If the magnetic field is high, then the interaction of accelerated protons with gas will dominate. On the other hand, if the magnetic field is low, the interaction of accelerated electrons with light is preferred. Crucially, as the electrons move away from the acceleration site, they will lose energy by emitting X-rays at a rate that depends on the strength of the magnetic field. The observed width of the X-ray emitting regions can therefore be used a probe of the magnetic field strength.

An artist’s illustration of the Chandra spacecraft in orbit. (Illustration: MSFC, Credit: NASA/CXC/SAO)

Resolving these emission regions at the distance of the LMC in sufficient detail requires a very powerful telescope, namely the Chandra X-ray Observatory. The combination of Chandra’s exquisite mirror and the Advanced CCD Imaging Spectrometer revealed the structure of the 30 Doradus C shell in unprecedented detail. This allowed the team to measure the widths of the emission region around the shell and determine a generally low magnetic field strength, suggesting that the VHE gamma-rays produced in 30 Doradus C predominantly arise from the interaction of accelerated electrons with ambient light.

Link to the publication: Astronomy and Astrophysics

For further information please contact:

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

New web archive with photographic plates from the Astronomical Collection at FAU now available online

2018 October 26

If you look up at the sky on a clear night you can see stars, lots of stars. Astronomical recordings from observatories let you see them in much greater detail. The Dr. Remeis Observatory owns approximately 40,000 historical photographic plates, a genuine treasure trove for anyone interested in stargazing. Together with Leibniz-Institut für Astrophysik Potsdam and the Universities of Hamburg and Tartu (Estonia), astronomers at FAU have now digitalised roughly 70,000 such glass plates and published them online at www.plate-archive.org. The project is being funded by the German Research Foundation (DFG).

All areas of the sky have been charted in the new web database – red means that an area of sky has been recorded very often, blue are the areas that have only been recorded very rarely. Thanks to the observations of the Bamberg Observatory, the southern sky has been particularly well covered. (Image: AIP/APPLAUSE)

More than 400,000 photographic plates are stored in the archives of German observatories, accounting for approximately one quarter of all the photographic plates that exist in the whole of Europe. They are not only valuable from a historical point of view, they are still highly significant for research even today, as astronomers can use them to track the movements and changes in brightness of stars over several decades. In addition, modern digitalisation techniques and software can be used to answer a whole range of new questions, allowing astronomers to investigate millions of stars much more objectively and accurately.

However, all this potential knowledge cannot be taken advantage of unless people are actually aware that such an image exists, and know when and how it was taken. This is exactly what the APPLAUSE database delivers – together with the image itself. A sizeable catalogue of over 70,000 digitalised photographic plates from the four observatories mentioned above is now available online, covering the years 1893 to 1998. Each individual scan is several hundred megabytes in size. The largest plates that measure 30×40 centimetres can be as big as one gigabyte.

Prof. Ulrich Heber will talk about the ‘Digitalisation of the Sky’ on the 10th of January as part of the Collegium Alexandrinum, which is open to the public.

In coordination with the release, the Remeis Observatory will host a conference with the title ‘Large surveys with small telescopes: Past, Present and Future (Astroplate III)‘ in March next year. Registration for the conference is now open.

This post is a short version of the full press release of the FAU. The full article on ‘Digitalisation of the Sky’ can be found here.

Access to the APPLAUSE database: www.plate-archive.org
Conference Webpage: https://www.sternwarte.uni-erlangen.de/large-surveys-2019/
Collegium Alexandrinum: http://www.collegium-alexandrinum.de/

For more information, please contact

Ulrich Heber
Ulrich.Heber@sternwarte.uni-erlangen.de
+49 951 95222 14

Bilateral ejecta jet observed in the remnant of the collapse of a massive star

2017 August 9

ROSAT All-Sky Survey image of the Vela SNR (red: 0.1 – 0.4 keV, green: 0.5 – 2.0 keV). The bright source in the upper right is the Puppis A SNR located in the background.
Credit: ROSAT Data Archive, Max-Planck-Institut für extraterrestrische Physik, Garching, Germany

When a massive star ends its life it explodes in a very energetic explosion called a supernova. The ejected stellar matter expands spherically and is in some cases also collimated into jets. If a jet points to us, the explosion is observed as a very intense flash of gamma-ray emission (called gamma-ray bursts, GRBs) due to relativistic beaming. Owing to their high luminosity, GRBs can be detected even if they occur in extremely distant galaxies.

Jets had so far only been resolved and studied in the remnant of the supernova Cassiopeia A, a bright young supernova remnant (SNR) located in our Galaxy. Based on a new observation using the X-ray telescope XMM-Newton, researchers at the Instituto Argentino de Radioastronomía (Argentina) and INAF-Osservatorio Astronomico di Palermo (Italy) discovered antipodal structures indicative of a jet in the nearby Vela SNR. The X-ray emission of these structures show a high abundance of Si, suggesting that the matter originated from the deepest layers of the star that exploded. The new results of this research, in which Prof. Dr. Manami Sasaki of the Friedrich-Alexander University Erlangen-Nürnberg is also involved, have been recently published as a highlight paper in “Astronomy and Astrophysics”.

For more information, please contact

Manami Sasaki
Manami.Sasaki@fau.de
+49 951 95222 19

Blue stars pulsating in the night sky

2017 July 3

Credit: Paweł Pietrukowicz

In the middle of the large Chilean Atacama desert, a team of Polish astronomers monitors millions of celestial bodies night after night with the help of a modern robotic telescope. In 2013, the team was surprised when they discovered, in the course of their survey, stars that varied much faster than expected. In the following years, the team including Dr. Marilyn Latour, an astronomer from the Dr. Remeis-Sternwarte Bamberg, the astronomical institute of the Friedrich-Alexander-University Erlangen-Nuremberg, studied the stars in more detail and concluded that they had discovered a new class of variable star. Their results have been recently published in Nature Astronomy (DOI: 10.1038/s41550-017-0166).

Many classes of star show brightness variations. Unlike our Sun, these stars are not stable; their surface oscillates, meaning that the surface expands and shrinks by a few percent. This is the case for the well-known Cepheids and RR Lyrae stars, which show oscillation periods ranging from a few hours to hundreds of days.

The researchers discovered a dozen of stars that seemed at first glance to vary in a very similar way to the Cepheids and RR Lyrae stars, but with much shorter (20-40 minutes) oscillation periods and their colour is much bluer. This indicates that the newly discovered stars are hotter and more compact. These properties were the motivation for the proposed acronym of the new class of variable stars: BLAPs – Blue Large-Amplitude Pulsators. The nature of these stars, however, remained a matter of speculation.

The nature of the newly discovered stars

The nature of the stars posted the researchers a riddle. At first, the astronomers assumed that BLAPs could be hot dwarf stars since they have similar oscillation periods. Hot dwarf stars are old stars approaching the end of their lives. They generate their energy via the thermonuclear fusion of helium into carbon. The Sun, being in an earlier phase of its life, is currently burning hydrogen into helium.

In order to find out whether BLAPs are actually hot dwarfs the researchers made observations with two of the largest telescopes. The astronomers were able to secure suitable spectra of some BLAPs using the large Gemini and Magellan telescopes, both located in the Chilean Atacama desert. Dr. Latour analyzed those spectra using sophisticated physical-numerical models. She showed that the light variations are due to temperature changes at the surface of the star. The temperature of the BLAPs turned out to be five time larger than that of the Sun, which is typical for hot dwarfs.
However, the BLAPs are significantly bigger than hot dwarfs, meaning that they form a new class of stars similar to hot dwarfs but with bloated envelopes. Why BLAPs oscillate like Cepheids and why they are bloated remains a puzzle, as well as their formation history. The mystery of the origin of the BLAPs needs to be solved by new investigations.

For more information, please contact

Marilyn Latour
Marilyn.Latour@fau.de
+49 951 95222 16

New Hypervelocity Binary Star

2016 April 11

A team of astronomers at the Friedrich Alexander University led by Péter Németh has discovered a binary star moving nearly at the escape velocity of our galaxy. There are about two dozen so-called hypervelocity stars known to be escaping the galaxy. While all of them are single stars, PB3877 is the first wide binary star found to travel at such a high speed. Additionally, the results of the new study challenge the commonly accepted scenario that hypervelocity stars are accelerated by the supermassive black hole at the galactic center. The findings are being published in the Astrophysical Journal Letters on April 11, 2016.

Take a look at the Keck Observatory News, watch the visualization or read the full journal article!

Best-Ever Snapshot of Black Hole Jets

2011 May 20

An international team, including NASA-funded researchers, using radio telescopes located throughout the Southern Hemisphere has produced the most detailed image of particle jets erupting from a supermassive black hole in a nearby galaxy.

“These jets arise as infalling matter approaches the black hole, but we don’t yet know the details of how they form and maintain themselves,” said Cornelia Müller, the study’s lead author and a doctoral student at the University of Erlangen-Nuremberg in Germany.

The new image shows a region less than 4.2 light-years across — less than the distance between our sun and the nearest star. Radio-emitting features as small as 15 light-days can be seen, making this the highest-resolution view of galactic jets ever made. The study will appear in the June issue of Astronomy and Astrophysics and is available online.

Read the full press release at NASA!

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