Posted on by Matt Williams

The Milky Way has an Inner Ring, Just Outside the Core

This image from the NASA/ESA Hubble Space Telescope reveals a spiral galaxy named Messier 95 (also known as M95 or NGC 3351). Located about 35 million light-years away in the constellation of Leo (The Lion), this swirling spiral was discovered by astronomer Pierre Méchain in 1781, and catalogued by French astronomer Charles Messier just four days later. Messier was primarily a comet hunter, and was often left frustrated by objects in the sky that resembled comets but turned out not to be. To help other astronomers avoid confusing these objects in the future, he created his famous catalogue of Messier objects. Most definitely not a comet, Messier 95 is actually a barred spiral galaxy. The galaxy has a bar cutting through its centre, surrounded by an inner ring currently forming new stars. Also our own Milky Way is a barred spiral. As well as hosting this stellar nursery, Messier 95 is a known host of the dramatic and explosive final stages in the lives of massive stars: supernovae. In March 2016 a spectacular supernova named SN 2012aw was observed in the outer regions of one of Messier 95’s spiral arms. Once the light from the supernova had faded, astronomers were able to compare observations of the region before and after the explosion to find out which star had “disappeared” — the progenitor star. In this case, the star was an especially huge red supergiant up to 26 times more massive than the Sun.

In the past century, astronomers have learned a great deal about the cosmos and our place in it. From discovering that the Universe is in a constant state of expansion to the discovery of the Cosmic Microwave Background (CMB) and the Big Bang cosmological model, our perception of the cosmos has expanded immensely. And yet, many of the most profound astronomical discoveries still occur within our cosmic backyard – the Milky Way Galaxy.

Compared to other galaxies, which astronomers can resolve with relative ease, the structure and size of the Milky Way have been the subject of ongoing discovery. The most recent comes from the Max Planck Institute for Extraterrestrial Physics (MPE), where scientists have found a previously undiscovered inner ring of metal-rich stars just outside the Galactic Bar. The existence of this ring has revealed new insights into star formation in this region of the galaxy during its early history.

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Posted on by Jason Major

X-rays Reveal a Stellar-Mass Black Hole in Andromeda

This image shows the central region of the Andromeda galaxy in X-rays, where the newly discovered ULX outshines all other sources. Image: Landessternwarte Tautenburg, XMM-Newton, MPE

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An ultraluminous x-ray source (ULX) previously spotted in the neighboring Andromeda galaxy by NASA’s Chandra observatory has now been revealed to be a stellar-mass black hole, according to researchers at the Max Planck Institute for Extraterrestrial Physics.

The black hole was the first ULX seen in Andromeda, as well as the closest ever observed.

Ultraluminous x-ray sources are rare objects, observed in the near and distant Universe in the outer regions of galaxies. Typically only one or two ULXs are seen in any one particular galaxy — if there are any seen at all.

The large distances to ULXs makes detailed observations difficult, and so their exact causes have been hard to nail down.

This particular x-ray source was first identified in late 2009 by Chandra and was followed up with observations by Swift and Hubble. Classified by researchers at the Max Planck Institute as a low-luminosity source, it actually outshined the entire Andromeda galaxy in x-ray luminosity!

Continued observations with Chandra and ESA’s XMM-Newton showed behavior similar to known x-ray sources in our own Milky Way galaxy: actively feeding black holes.

“We were very lucky that we caught the ULX early enough to see most of its lightcurve, which showed a very similar behavior to other X-ray sources from our own galaxy,” said Wolfgang Pietsch from the Max Planck Institute for Extraterrestrial Physics. The emission decayed exponentially with a characteristic timescale of about one month, which is a common property of stellar mass X-ray binaries. “This means that the ULX in Andromeda likely contains a normal, stellar black hole swallowing material at very high rates.”

It’s estimated that the black hole is at least 13 times the mass of the Sun.

(Related: Stellar-Mass Black Hole Blows Record-Speed Winds)

Continued observations of the ULX/black hole will attempt to observe another outburst similar to the 2009 event, although if this black hole is anything like those observed in our galaxy it could be years before another such event occurs. Still, our relatively clear view of the Andromeda galaxy unobscured by intervening dust  and gas offers a chance to perhaps spot other potential x-ray sources residing there.

Read the report from the AlphaGalileo Foundation here, or on ScienceDaily here.

The first MPE team’s paper can be found here.