Bad astronomy | A black hole tore a star and ate it, revealing its mass and rotation

If you were to bet on a star against a black hole, you would bet on the black hole to win every time.

Corn How? ‘Or’ What he wins tells us a lot. Your standard problem stellar mass black hole (one with, say, 5 to 100 times the mass of the mass of the Sun) would properly be (and tide) remove the material from the star and eat it slowly over time. A supermassive black hole (with over 100,000 times the mass of the Sun) could eat an entire star at once, especially those at the top of the weight scale with billions of solar masses.

But intermediate mass black holes are different. They are sloppy eaters and tear the star to shreds before gobbling up the vaporized meal. It releases an overwhelming amount of energy, easily – easily – a billion times the brightness of the Sun. These are ridiculously violent catastrophes, so of course astronomers have given them the lame name of tidal disturbance events, or TDE.

In 2006, astronomers saw just such an event: a huge eruption of high-energy X-rays from a location just outside of a galaxy about 750 million light-years from Earth. A Hubble image located the shard’s position toward a small spot of light outside the galaxy, likely either a globular cluster or the remains of a dwarf galaxy that had been eaten by the larger galaxy.

I wrote an article with all the basic information you need in April 2020 (and also, even earlier, I wrote an article about this event in 2018). The event, called 3XMM J215022.4−055108 (let’s just call it J2150), was observed by the Chandra X-ray Observatory and XMM-Newton X-ray Observatory, and using models of how stars are torn and eaten, the mass of the black hole turned out to be about 50,000 to 100,000 times that of the Sun.

It was a big deal. This would make it an intermediate mass black hole, and while many interesting and compelling observations indicate that these types of black holes exist, none have ever been solidly confirmed.

A team of astronomers reassessed this event, using updated models, and find that the black hole is probably even smaller, around 17,500 solar masses, much less than previously thought, and placing it firmly in the range of intermediate masses. They also find that it spins quickly but not as fast as you might expect, so weird things are brewing.

A black hole of intermediate mass – let’s call them IMBH to save my poor tired fingers – is tearing a star apart by the tides. Gravity weakens with distance, so as a star approaches an IMBH, the nearest side of the star feels a much stronger gravitational pull than the far side of the star. . This effect is what we mean by tides, and it gets stronger as the star gets closer. If he gets too close, riiiiiip. The star is torn.

The ex-star is now an extremely hot and long gas loop around the IMBH. It is dragged into a flat disc called an accretion disc, which becomes infernally hot and slowly feeds the black hole. The light from this flat disk can be used to measure the mass of the disk, but so far it has only worked well for stellar mass black holes and supermassive holes.

This is how they found that the mass was only 17,500 solar masses. Even with the inherent uncertainty in their measurements and models, this remains a real IMBH.

But they can do more. Black holes are spinning. It’s a strange concept, because they don’t really have a surface. But as matter falls in it, it spirals like water flowing down a sewer. This adds angular momentum to the black hole, which is similar to the spin. Also, and this part is really scary, when the black hole spins it pulls the web of space-time around it. If you were near a black hole and tried to fall straight into it, you would always end up circling around it because the space itself hisses around it (as if a rubber duck starts circling around). of the drain because it is carried by the water in the tub).

Scientists quantify this spin using a range from 0 (no spin) to 1 (spinning as fast as possible, essentially at the speed of light). A black hole that grows by eating, for example, gas from a large galaxy will tend to have an extreme rotation, close to 1, because this gas tends to rotate around the black hole in the same direction (again a times like water in a drain), adding to its angular momentum. Whoever grows up eating random stars that can come from any direction tends to have a weaker rotation, around 0.1 to 0.3.

Using the same models they did to get the mass and carefully examine the x-rays of the event, astronomers find that IMBH has a spin of 0.8. It’s weird. Not too fast, but not really slow either. Maybe it was spinning fast at first, but then started eating on stars like this last one, and that material fell the wrong way and slowed down the spin a bit (like trying to force water into a drain against the main rotation will slow down the movement of that rotation).

Either way (again if they’ve done it right), this is the first time an IMBH’s rotation has been measured. That’s great.

Irritating, it’s hard to call it evidence of the existence of IMBHs, but it’s pretty convincing, and it certainly looks more and more like how to bet.

These are rare events – only a handful have been detected – and only detected because we have large telescopes scanning the sky looking for short, bright events like this. We are improving all the time to find and understand things like this. There are a lot of amazing things going on in the Universe around us, and I’m happy we’re keeping our eyes open to see them.

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