Astronomers find black hole closest to Earth, and it has a Sun-like companion star

Astronomers have found the closest known black hole candidate to Earth, a cool beast about ten times as massive as the Sun, just 1,570 light-years away from us.,, It was found through the movements of its Sun-like stellar companion, but how it happened is a head-scratcher [link to paper],

There are likely a hundred million black holes in our galaxy alone, but they are difficult to find. The easiest way is if they are in a binary system with a companion star, and they are so close together that material is stripped of the star and collapses into the black hole. As it piles up outside that last big step The material heats up and emits a lot of high-energy radiationBasically declares the existence of black holes.

But if the black hole is alone, or in a binary with the star, which is orbiting further, it is silence, which makes it difficult to detect. The thing about black holes is that they are blackSo They can only be detected through their immense gravity,

Still, it can reveal them if the conditions are right.

In the case of this new, they were. But still, it is a difficult find.

Phil Platt Bad Astronomy art_imbh_tde

Phil Platt Bad Astronomy art_imbh_tde

Artifact of a star torn apart by an intermediate-mass black hole. Material falls into the deprivation hole, creating lots of X-rays and allowing astronomers to learn a lot about black holes. credit: ESA/Hubble, M. Kornmeiser

The Gaia spacecraft is a European Space Agency mission that carries about two . maps the locations of One billion Stars, Not only does it map their position in the sky to unprecedented accuracy, but it also measures their speed and colors.

If two stars orbit each other, each will trace a very small ellipse in the sky, In most cases this physical motion is too small to be observed, but for relatively close binary systems with wide orbital separations, Gaia can observe this change in the position of a star over time.

There are about 170,000 such fascinating binary stars in the Gaia database. Here the astronomers looked for those with unusually large speeds – indicating that one of the stars is indeed very massive – but where the overall light from the system was less than expected. Massive stars are bright, so if the motion of the binary indicates that one is massive but severely underpowered, it could be a black hole.

They found some promising candidates, but after more careful analysis found only one that seemed solid: the star Gaia DR3 4373465352415301632 – they call it Gaia BH1 (“Gaia Black Hole 1”) for convenience. It is a star in the constellation Ophiuchus with color and brightness indicating that it is similar to the Sun, though slightly cooler and less massive. Gaia directly measures its distance from us as 1,570 light-years through parallax, which is consistent with its luminosity.

If it weren’t for the fact that the star is forming a small ellipse in the sky this would be completely unremarkable. There are no other stars nearby that could be related to it, yet it is moving back and forth across the sky with a period of 185.6 days.

They obtained the spectra of the star using several different ground-based telescopes, and used them to measure star doppler shift Circling around his unseen companion. The velocity of the star is quite high, more than a hundred kilometers per second, indicating that the companion object is indeed very heavy. They find that its mass is 9.8 ± 0.2 times the mass of the Sun., and that is clinical. A normal star that would be unprecedented in mass would be several thousand times brighter than a Sun-like star that would swallow it whole.

The fact that the object is very massive but completely dark can only be understood if it is a black hole. It’s not technically confirmed, so we’d have to call it a candidate, but looking at the data I’d bet it’s a black hole.

Artwork showing a cool black hole on a starry background.  Credits: NASA, ESA, D. Coe, G. Bacon (STScI)

Artwork showing a cool black hole on a starry background. Credits: NASA, ESA, D. Coe, G. Bacon (STScI)

Artwork showing a cool black hole on a starry background. Credit: NASA, ESA, D. Coe, G. Bacon (STScI)

This is also a strange system. We know of other black holes in orbit with normal stars, but none have been widely isolated; The star is almost as far from the black hole as Mars is from the Sun. This is actually a problem because of the way black holes are formed.

It must have initially been a massive star about 20 times the mass of the Sun, a mighty monster. Only a few million years after its birth, the fuel at its core would have run out, while the low-mass star was still on its way to becoming a normal star. Then the giant star would have swelled into a giant red supergiant, Big enough to physically swallow a small star, it is called common envelope Binary stage. In general, the outer layers of the more massive star are pushed out by the motion of the lower-mass star, and in turn the two stars move upward as they spin together, although in this case the other is probably too efficient to do so. was very light.

It’s hard to get a star so far away from that scenario; Normally they would be only a few million kilometers away. At some point the more massive star explodes as a supernova, losing some of the mass, which can lead to the other star being further… but not immensely.

It’s possible that there used to be a third star in the system, and that could fiddle with enough orbits to explain the system, but that situation is finicky and has a narrow set of parameters to work with. It is also possible that the system was born in a star cluster, and that the gravitational effects of other stars during the pass may have cast the binary into what we see today.

Now the big question is, how common are such systems? One has previously been observed in a nearby galaxy – The Gaia BH1 paper’s Principal Investigator Karim al-Badri also worked on finding this first one – but the fact that it’s closer to us means these systems are common. The Milky Way is 120,000 light-years across, so even if these things are rare, the chances of the closest being so close would be extremely small. If they’re common, Gaia is likely to find many more in the future; The longer it observes the same star over and over, the easier it is to detect their motions.

It is ironic that we know of thousands and thousands of black holes in distant galaxies millions and billions of light-years away, because they are so massive and dissipating really enormous amounts of energy, yet our own galaxy Most of the black holes in the universe are completely invisible to us.

now. they are invisible Now he, but we’re getting better all the time at finding them. They are dark, but they cannot hide forever.

, I will note that this is still a long way from human point of view — 15 quadrillion kilometer! – So it’s not a threat to us.



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