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While scanning the heart of the galaxy, astronomers found the fastest star ever. This thing is tearing up space; at one point in its orbit it is moving at a terrifying speed of 24,000 kilometers per second – over 85 million kilometers per hour!
This is 8% the speed of light.
Holy relativistic acceleration! How can a star howl in space so quickly?
Well it helps to dive inside 1.9 billion kilometers of a supermassive black hole.
Oh yeah, there is a story here.
At the center of our galaxy, the Milky Way, is a huge black hole with a mass four million times that of the Sun. All major galaxies have one.
This black hole, called Sgr A * (literally, “Sagittarius A-star”) is not alone. Around it are a variety of objects, including dozens of massive stars. These revolve around the black hole quite close, and the black hole’s enormous gravity causes them to rock at extremely high speed. The evolution so fast that the changes in their positions can be observed in just a few months.
Not that it’s easy to see. We’re about 27,000 light-years from the center of the Milky Way, so even though these stars are bright, the distance reduces their brightness. In addition, there is a lot of dust between us and the galactic center, which makes them even more difficult to observe. One way around this is to look into infrared light, which pierces dust better than optical light, the one we see.
It also helps if you use one of the huge behemoths of the 8.2-meter Very Large Telescope in Chile. Using a pair of extremely sensitive, keen-eyed cameras (called SINFONI and NACO), astronomers have been mapping these stars for many years. One in particular, called S2, has such a close and definite orbit that it was used to measure the mass of the black hole in the first place.
But several stars have now been spotted in even tighter orbits. One, S62, recently passed very close to the black hole – less than 3 billion kilometers, closer than Neptune is to the Sun! – produce all kinds of funny observations and science. For comparison, the black hole itself is about 24 million kilometers in diameter.
In the new document, astronomers announce a recently discovered star called S4714. Its orbit is similar to that of the S62: very elliptical, and the lower extremely near the black hole. But it gets even closer to the S62, at around 1.9 billion kilometers*. It is closer than Uranus is to the Sun.
When S62 flies past the black hole, it is moving at around 6.7% of the speed of light, but S4714 beat it, just absolutely cannon in front of Sgr A * at 8% of the speed of light.
I won’t lie to you. This makes the hair at the back of the neck stand up. This is quick.
I mean, it’s fast enough to cross the continental United States in a fifth of a second. Fast enough to get from Earth to the Moon in about 16 seconds (it took more than three days for the Apollo spacecraft to get this far). The Parker solar probe, when it is closest to the sun. travels at over 100 kilometers per second, the fastest spacecraft ever. This star moves well more than 200 times faster.
Ye, and may I add, gads.
It’s more than just a record. On the one hand, this near relativity of the black hole rears its head. There is an effect called frame sliding which changes the orientation of the orbit, causing it to rotate. We have seen that the orbits of these stars do this, which helps us better understand the relativistic effects of the black hole on near space. Since S4714’s orbit only lasts 12 years, this means that astronomers can also observe this effect in near real time.
S4714 is so close to Sgr A * and so faint that even the largest infrared telescopes in the world have trouble spotting it among the crowds of stars at this point in the sky. Still, it does imply that there may be stars even closer, perhaps just less massive and too faint to spot. However, there is a limit to their proximity, without tearing apart. It will be interesting to know how close these stars are. Hopefully in the future gigantic telescopes will have an even better view.
I remember when the first stars were seen near the black hole and how their motion was used to measure its mass and our distance from it. It wasn’t that long ago, but we’ve come a long way since then. It makes me wonder what else we will see in this curious menagerie. And what records will be broken next.
* The orbit of the star is not perfectly determined and presents a great uncertainty. The closest approach is actually 1.9 billion ± 1.4 billion kilometers, so it may actually get closer… or it may not be that close. For this article, I’m assuming an approach closest to 1.9 billion.
Ergosphere tip for Bryan gaensler.
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