Astronomers have had a rare glimpse into the heart of the Milky Way thanks to an errant star expelled from the galactic centre.
At the middle of our galaxy is a supermassive black hole, closely surrounded by a group of hundreds of stars. Slightly further out is a larger disc of stars, and further out still is an even larger star group, called the nuclear star cluster (NSC).
So far, astronomers have only managed to catch glimpses of any of these stellar objects because a shroud of thick dust absorbs much of their light before it can reach us, making it difficult to study the elements they contain and how and when they formed.
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Now, at the National Astronomical Observatory of Japan in Tokyo and his colleagues have managed to get a better look at one of these stars. They were combing through data from the Gaia space telescope, a detailed catalogue of billions of stars in our Milky Way, when they spotted one speeding away from the galactic centre at around 500 kilometres per second.
When moving this fast, they are known as hypervelocity stars聽and can achieve their high speeds by coming close to a supermassive black hole, but astronomers haven鈥檛 been able to study the chemical makeup of one from our galactic centre before.
Using an infrared spectroscope on the Magellan Clay Telescope in Chile to analyse light coming from this speeding object, Hattori and his colleagues found that the star鈥檚 composition closely matches what we know about the elements that make up stars in the NSC.
They are now making further observations using visible light from the star, which they hope will tell us even more about the mysterious environment in which it formed. 鈥淧reviously, if we wanted to understand the galactic centre, we had to direct telescopes [there], but now with the emergence of these hypervelocity stars, we can point the telescope to random directions away from the galactic centre,鈥� says Hattori.
It remains to be seen whether the star truly came from the galactic centre, says at the University of Manchester, UK. 鈥淚t鈥檚 clear it has travelled from elsewhere in the galaxy, and has an orbit that could well have come from the galactic centre, but they can鈥檛 be fully certain about exactly where it came from.鈥�
In separate work, at Lund University in Sweden and his colleagues peered into the galactic centre using an infrared instrument on the Gemini South telescope in Chile. They identified 19 elements 鈥� including fluorine, sodium and aluminium 鈥� most of which hadn鈥檛 been detected in the NSC before.
鈥淭wo weeks ago, our knowledge about the galactic centre鈥檚 chemical data was limited to a few key elements such as iron, magnesium, silicon and calcium,鈥� says Hattori. Now our understanding has hugely increased, which will help astronomers work out how these stars formed, he says.
This type of survey is difficult because so much light is absorbed by the shroud of dust, says Zijlstra. 鈥淚t鈥檚 very hard to find the stars, to get enough [light] to do these things, so it鈥檚 quite impressive. It probably is important in finding out exactly how this nuclear disc formed,鈥� he says.
arXiv
arXiv
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