Stars, supernovae, black holes and stellar remnants

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Astronomers have reported the discovery of S301, the fastest known star in our galaxy, which also now becomes the closest yet observed orbiting Sagittarius A*, the supermassive black hole at the centre of the Milky Way. The star completes an orbit every 8.7 years and reaches about 25,000 km/s, or 8.5% of light speed, at its closest approach. Its unusually tight orbit may enable a direct measurement of Sagittarius A*'s spin within about a decade.

https://www.nature.com/articles/s41586-026-10894-w

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Quiet Black Holes with a Stellar Companion Raise Questions About How They Form
By Brian Koberlein
September 7, 2026

Introduction:

(Universe Today) Active black holes are pretty easy to detect. Their superheated accretion disks emit bright x-rays, and the jets streaming from their poles are easily seen at visible and radio wavelengths. But most stellar-mass black holes are inactive. They either drift through the galaxy alone or orbit a companion star without consuming its material. We can't observe inactive black holes directly. We can only observe their effect on nearby objects. We currently know of three such black holes thanks to the Gaia spacecraft.

The main mission of Gaia is to map the positions and motions of more than a billion stars in our region of the Milky Way. To achieve its goal, the motion measurements must be very precise. Precise enough that we can detect small wobbles in a star's motion. Usually this means the star has a planet, and the gravitational tug of the planet causes the star to wobble. But in at least three cases the gravitational tug is so large that the companion must have a stellar mass. If it were a star, Gaia would see it. Since Gaia doesn't, the companion must be a black hole.

Each of the quiet black holes we've discovered this way has a small stellar companion. This means that in the past these were asymmetrical binaries, meaning that one of the stars was much larger than the other. The remnants of the large stars became black holes, forming the systems we see today.

In one of these systems, Gaia BH3, the system is a fairly wide binary just as we would expect. But the other two, BH1 and BH2, the binaries are much closer. This poses a challenge as to how they formed. When a large star dies, it expands tremendously. A close-orbiting companion would be engulfed by the dying star, causing the two of them to merge before the system becomes a single black hole. Given the orbits of the companions in BH1 and BH2, how did they survive? One idea is a process known as Roche Lobe Overflow.

Read more here: https://www.universetoday.com/articles ... ey-form

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Be the first on your block to discover a black hole:

If You Want to Discover a Missing Black Hole in Our Galaxy, This Is Your Chance
By Dr. Alfredo Carpineti
October 2, 2026

Introduction:

(IFL Science) The closest black hole to Earth is a whopping 1,600 light-years away, one among the 50 stellar-sized black holes we know of in the Milky Way. There should be around 100 million out there, so to start chipping away at our ignorance, a new citizen science project is giving anyone the opportunity to find more.

Additional Extract:

Human intelligence needed

The team is using data from NASA’s planet-hunting telescope TESS, or the Transiting Exoplanet Survey Satellite. They have trained a neural network – a type of artificial intelligence – to find potential candidates among 15 million light curves from as many stars.

The impressive system was able to find 1 million candidates in just one week, but human eyes are needed to actually work out which ones are reasonable candidates. That's because there are many other phenomena that can periodically increase and decrease a star's brightness.

“It's really simple,” Dr. McMaster told IFLScience. “We show people examples of what it is they need to look at. Every single person who takes part might be the one to find the first of this new population of black holes that we haven't found before.”

Read more here: https://www.iflscience.com/if-you-want ... ce-84831

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Astronomers catch a star slowly snacking on a brown dwarf, 300 light years away

The discovery reveals a new way that stars and planetary companions can interact.

October 5, 2026

Like Earth, most planetary bodies circle their star in stable, detached orbits. These companionable systems can suddenly change when a planet comes too close to its star. In such a close encounter, a star can pull the planet in and swallow it whole.

Across the galaxy, astronomers have seen plenty of stable, detached planetary systems. They have also observed a handful of stars quickly engulfing their planet. Now, for the first time, scientists have spotted a system that is striking a curious balance between the two extremes. And it’s revealing a new way that stars can interact with planetary companions.

In a paper appearing today in Nature Astronomy, scientists at MIT and elsewhere have discovered a star leisurely snacking on a closely orbiting brown dwarf — a planet-like object that is more massive than a planet yet not quite as big as a star.

The new system, named ZTF J0440+2325, is within the Milky Way galaxy, roughly 300 light years from Earth, and represents the first observation of a low-mass object that is slowly and steadily consuming material from another low-mass object.

The rate at which the star is feeding from the brown dwarf suggests that this slow stellar cannibalism could carry on for hundreds of thousands, or even billions of years.

https://news.mit.edu/2026/astronomers-c ... dwarf-1005



Credit: Aaron Householder (MIT)

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