All-clear in space: Cuddling inside a nebula does not have to end in a catastrophe

June 24, 2020
Cuddling inside a nebula
Artist's impression of the two merging central stars inside the planetary nebula Henize 2-428 (Image Credit: Nicole Reindl).

Supernova type Ia explosions are important astronomical tools to measure cosmic distances. However, the nature of the progenitor systems that leads to this kind of explosion is still elusive. The only definite candidate for a progenitor system was the binary nucleus nestled in the heart of the planetary nebula Henize2-428. The two central stars are actually so close that they even share a common envelope and will merge within a few hundred million years. Back in 2015, an article published in Nature claimed a total mass of the two stars of about 1.8 times that of the Sun, which is high enough for triggering a supernova type Ia explosion. Contrary to this, a careful re-analysis of the system now shows that no supernova explosion is to fear. The study was led by Nicole Reindl, open-topic research fellow in our group, and the results of this work have now been published as a highlight-paper in Astronomy&Astrophysics. Together with her international team, which also includes two other members of our group, she revealed that a contamination of the observations by diffuse interstellar bands has led to a significant overestimation of the masses of the two central stars. It was found that the total mass of the system actually only slightly exceeds one solar mass, far too low to trigger a supernova Ia explosion. Thus, the race to find a definite supernova type Ia progenitor system is now re-opened.
Press release: University of Potsdam

New version of the hot subdwarf catalog

March 1st, 2020
Hot subdwarfs
Sky distribution of the objects in the catalog in equatorial coordinates (Image Credit: A&A).

Stephan Geier's updated version of the hot subdwarf catalog has now been published in Astronomy&Astrophysics. This new version of the catalog was motivated by substantial new discoveries of hot subdwarfs by ongoing spectroscopic surveys and the availability of new all-sky data from ground-based photometric surveys and the Gaia mission Data Release 2. The catalog contains 5874 unique sources including 528 previously unknown hot subdwarfs and provides multi-band photometry, astrometry from Gaia, and classifications based on spectroscopy and colours. In addition to that atmospheric parameters of 2187 stars and radial velocities of 2790 stars from the literature are provided.

When David poses as Goliath – A stripped helium star solves the massive black hole mystery

January 10th, 2020
Image Credit: CC0 Public Domain

Stellar black holes form when massive stars end their life in a dramatic collapse. Observations have shown that stellar black holes typically have masses of about ten times that of the Sun, in accordance with the theory of stellar evolution. Recently, a Chinese team of astronomers claimed to have discovered a black hole as massive as 70 solar masses, which, if confirmed, would severely challenge the current view of stellar evolution. The publication immediately triggered theoretical investigations as well as additional observations by other astrophysicists. Among those to take a closer look at the object was a team of astronomers from the Universities of Erlangen-Nürnberg as well as some members of our group. They discovered that it may not necessarily be a black hole at all, but possibly a massive neutron star or even an 'ordinary' star. The results have now been published as a highlight-paper in Astronomy&Astrophysics.
Press releases: University of Erlangen, University of Potsdam

Stars on the Run II

September 1st, 2019
Stars on the Run II
Conference group picture.

From August 25 to 30 2019 we hosted the Stars on the Run II conference. This workshop aimed
to understand the origin of run-away and hyper-velocity stars and to put constraints on the
various proposed acceleration scenarios, but also to make use of these extreme stars as probes
for addressing diverse astrophysical questions.