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The Black hole at centre of Milky Way is forging new star-gas hybrid objects


By: Tech Desk | New Delhi |

Updated: January 16, 2020 2:23:32 pm


black hole responsible for new stars, Sagittarius A*, milky way galaxy, black hole, new star, gas star hybrid, university of california, ghez, ciurlo Orbits of the G objects at the centre of our galaxy, with the supermassive black hole, indicated with a white cross. Stars, gas and dust are in the background. (Image: Anna Ciurlo, Tuan Do/UCLA Galactic Center Group)

We know that our Milky Way galaxy is glued together by a supermassive black hole Sagittarius A* at its centre, buried deep in the constellation Sagittarius constantly pulling stars, dust, and other matters inward. However, a new study suggests that the Sagittarius A* might not be only devouring things but actually responsible for the creation of new kind of stars that are quite different from the stars we know.

Astronomers from UCLA’s (University of California — Los Angeles) Galactic Center Orbits discovered the new class of objects at the centre of our galaxy not far from Sagittarius A*. The study published in the journal Nature mentions that these anomalous objects look like oblong blobs of gas several times more massive than Earth but behave like small stars capable of passing perilously close to the black hole’s edge without being ripped to shreds.

“Black holes may be driving binary stars to merge,” study co-author and a professor of astrophysics at the UCLA Andrea Ghez said in a statement. “It is possible that many of the stars we’ve been watching and not understanding may be the end product of mergers.”

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Given the shape, orbits, and interaction of these six objects (dubbed G1 to G6) with Sagittarius A*, researchers believe that each G object is a pair of binary stars (two stars that revolve around each other) that got smashed together by the black hole’s gravity millions of years ago and still spilling out clouds of gas and dust in the messy aftermath of the collision.

“The new objects look compact most of the time and stretch out when their orbits bring them closest to the black hole. Their orbits range from about 100 to 1,000 years,” said lead author Anna Ciurlo, a UCLA postdoctoral researcher.

The first G-objects (G1) was discovered in 2005 by Ghez’s research group at the centre of our galaxy and in 2012 astronomers in Germany made a puzzling discovery of a bizarre object named G2 that made a close approach to the Sagittarius A* in 2014. At the time, Ghez and her research team believe that G2 is most likely two stars that had been orbiting the black hole in tandem and merged into an extremely large star, cloaked in unusually thick gas and dust.

black hole responsible for new stars, Sagittarius A*, milky way galaxy, black hole, new star, gas star hybrid, university of california, ghez, ciurlo The centre of the Milky Way galaxy, with the supermassive black hole Sagittarius A* (Sgr A*), located in the middle, is revealed in these images. (Image: NASA)

“At the time of closest approach, G2 had a really strange signature,” Ghez said. “We had seen it before, but it didn’t look too peculiar until it got close to the black hole and became elongated, and much of its gas was torn apart. It went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it’s getting more compact again.”

Ghez’s research group later reported the existence of four more objects they called G3, G4, G5 and G6. The researchers found out that while G1 and G2 have similar orbits, the other four have very different orbits.

“Mergers of stars may be happening in the universe more often than we thought, and likely are quite common,” Ghez said. “Black holes may be driving binary stars to merge. It’s possible that many of the stars we’ve been watching and not understanding may be the end product of mergers that are calm now. We are learning how galaxies and black holes evolve. The way binary stars interact with each other and with the black hole is very different from how single stars interact with other single stars and with the black hole.”

Researchers noted that while the gas from G2’s outer shell got stretched dramatically, its dust inside the gas did not get stretched much. “Something must have kept it compact and enabled it to survive its encounter with the black hole,” Ciurlo said. “This is evidence for a stellar object inside G2.”

“The unique dataset that Professor Ghez’s group has gathered during more than 20 years is what allowed us to make this discovery,” Ciurlo said. “We now have a population of ‘G’ objects, so it is not a matter of explaining a ‘one-time event’ like G2.”

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Researchers have already identified a few other candidates that may be part of this new class of objects, and are continuing to analyze them. Ghez noted that the centre of the Milky Way galaxy is an extreme environment, unlike our less hectic corner of the universe. He believes that the research will help understand what is happening in the majority of galaxies.

“The Earth is in the suburbs compared to the centre of the galaxy, which is some 26,000 light-years away,” Ghez said. “The centre of our galaxy has a density of stars 1 billion times higher than our part of the galaxy. The gravitational pull is so much stronger. The magnetic fields are more extreme. The centre of the galaxy is where extreme astrophysics occurs — the X-sports of astrophysics.”

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Updated: January 18, 2020 — 2:20 am

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