A rogue black hole roaming our galaxy could have just been confirmed

(ORDO NEWS) — The first detection of a black hole drifting in the Milky Way earlier this year has just received an important confirmation.

A second group of scientists, conducting a separate independent analysis, came to almost the same conclusion, which adds weight to the idea that we have potentially identified a rogue black hole roaming the galaxy.

Led by astronomers Casey Lam and Jessica Lu from the University of California at Berkeley. however, the new work came to a slightly different conclusion. Given the mass range of the object, it could be a neutron star rather than a black hole, according to a new study.

However, in any case, this means that we may have a new tool to search for “dark” compact objects that are otherwise undetectable in our galaxy, by measuring how their gravitational fields warp and distort the light of distant stars as they pass in front of them, which is called gravitational microlensing.

“This is the first free-floating black hole or neutron star detected using gravitational microlensing,” says Lu.

“With the help of microlensing, we can examine these lonely compact objects and weigh them. have opened a new window into these dark objects that cannot be seen otherwise.”

Theoretically, black holes are the collapsing cores of massive stars that have reached the end of their lives and are ejecting their outer material. These black hole progenitor stars, more than 30 times the mass of the Sun, are thought to have a relatively short lifespan.

Therefore, according to our best estimates, there should be between 10 million and 1 billion. stellar-mass black holes drift peacefully and silently through the galaxy.

But black holes are called black holes for a reason. They don’t emit light that we can detect unless some material falls on them, a process that generates X-rays from the space around a black hole. So if a black hole is just hanging around doing nothing, we have almost no way of detecting it.

Nearly. A black hole has a strong gravitational field so powerful that it distorts any light passing through it. For us as observers, this means that we can see a distant star brighter and in a different position than usual.

On June 2, 2011, that is exactly what happened. Two separate microlensing surveys, the Optical Gravitational Lensing Experiment (OGLE) and Microlensing Observations in Astrophysics (MOA), independently recorded an event that peaked on July 20.

This event has been named MOA-2011-BLG. -191/OGLE-2011-BLG-0462 (abbreviated as OB110462), and because it was unusually long and unusually bright, scientists decided to take a closer look at it.

“How long the brightening event lasts, a hint of how massive the lens in the foreground is refracting the light of a star in the background,” explains Lam.

“Long events are most likely associated with black holes. However, this is not a guarantee, because the duration of the brightening episode depends not only on how massive the foreground lens is, but also on how fast the foreground lens and the background star are moving relative to each other.

“However, by measuring the apparent position of a star in the background, we can confirm whether the lens in the foreground is indeed a black hole.”

A rogue black hole roaming our galaxy could have just been confirmed 2
An illustration showing how Hubble sees a microlensing event

In this case, the region was observed on eight separate occasions using the Hubble Space Telescope up until 2017.

From a deep analysis of this data, a team of astronomers led by Kailash Sahu of the Space Telescope Science Institute concluded that microlensing was the culprit. The black hole, which has a mass of 7.1 times the mass of the Sun, is located at a distance of 5153 light-years from us.

Lu and Lam’s analysis now adds more Hubble data as recently as 2021. Their team found that the object is somewhat smaller, between 1.6 and 4.4 solar masses.

This means that the object could be a neutron star. It is also the collapse of the core of a massive star that started between 8 and 30 solar masses.

The resulting object is supported by something called neutron degeneracy pressure, whereby the d neutrons don’t want to occupy the same place; this prevents it from collapsing completely into a black hole. Such an object has a mass limit of about 2.4 times the mass of the Sun.

Interestingly, no black holes below about 5 times the mass of the Sun have been found. This is called the bottom mass gap. If the work of Lam and her colleagues is correct, this means that we can detect an object with a smaller mass gap, which is very tempting.

The two teams returned with different masses for the Lensing Object because their analyzes produced different results for the relative motion of a compact object and a star with a lens.

Sahu and his team found that the compact object is moving at a relatively high speed of 45 kilometers per second, as a result of a birth shock: a one-sided supernova explosion can accelerate the collapsed core, accelerating it.

Lam and her colleagues, however, got 30 kilometers per second. This result, they say, suggests that perhaps a supernova explosion is not required for the birth of a black hole.

It is not currently possible to draw a firm conclusion from OB110462 which estimate is correct, but astronomers expect to learn a lot from the discovery of more such objects in the future.

“Whatever it is, this object is the first discovered remnant of a dark star wandering the galaxy without another star,” says Lam.


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