Wednesday , March 3 2021

Astronomers have mapped out the spectacular flow of a stellar explosion

Material accelerated from the place of a star explosion was discovered in a star-forming cloud.

This is only the second time such molecular currents have ever been clearly seen, but it could help astronomers understand how the most massive stars begin their lives.

In the 1980s, astronomers discovered something strange in the star-shaped Orion Nebula: streams of dense molecular gas, moving rapidly through space. When these streamers are waved, they appear to originate at one point.

Since then, molecular flows have been discovered in many star-forming regions. They are thought to play an important role in the formation of low-mass stars, and drive the excess angular momentum that would otherwise cause the baby stars to rotate themselves into oblivion.

Orion’s exports, however, were unique. Molecular currents in low-mass stars are bipolar; That is, only two of them fire in opposite directions. The flows in Orion were greater … and they were found in an area where much more massive stars formed – 10 times the mass of the sun.

w28A combination of X-rays, radio and an optical image of the W28, the area’s parent compound. (NASA / ROSAT; NOAO / CTIO / PF Winkler et al; NSF / NRAO / VLA / G. Dubner et al.)

Now, we do not know as much about the formation of huge stars as about the small ones in them. Massive star nurseries are rarer and tend to be more remote, making them difficult to see. So astronomers thought that perhaps the flow of Orion could yield clues.

However, there was nothing in the source of the streams – no massive baby star. This could imply a number of explosive scenarios, such as a merger between two massive infant stars, or a gravitational energy released by the formation of a massive massive binary. But with only one observation of its kind, it is difficult to make a decisive decision.

To try and learn more about this phenomenon, a team of astronomers led by Luis Zapeta of the National Autonomous University of Mexico decided to make one of our most powerful radio telescopes, the ATM A / M (A / B) sub-millimeter, known. Star nursery.

w28 lieFalse color image of W28. (NRAO / AUI / NSF and Brogan et al.)

G5.89−0.39, also known as W28 A2, is 9,752 light-years away. It contains a bright ultra-compact hydrogen cloud and expands like a shell and strong molecular currents. Zapata and his team have previously noted that these six wires appear to directly point to the center of the hydrogen cloud, but their results have not been unequivocal.

ALMA cleared this ambiguity literally. He identified dense streamers based on the wavelength emission of a millimeter of carbon dioxide and silicon monoxide.

Flows(Zapata et al., ApJL, 2020)

Astronomers have been able to detect 34 molecular streamers approaching radially from the heart of the cloud, accelerating outward. Based on their speeds up to 130 kilometers per second, the flows are about 1,000 years; Every explosion that created them occurred about a thousand years ago.

They are not as powerful as the currents you expect from a supernova explosion, which occurs when a massive star dies. In addition, as will also be seen in the case of Orion, there was no star in the center – only an area of ​​ionized gas, possibly the result of heating during an explosive event.

If there was a star (or number of stars) associated with the event that produced the flows, it could have been ejected from the region.

Because massive stars are always formed in clusters, such interactions are perhaps quite common, which in turn can shed some light on massive star formation. If two proto-stars merged, they would most likely end up in one much larger star.

Based on Orion flow, G5.89 flow and the marginal discovery of what could be a similar flow in a star-forming region known as the DR-21, the team estimates that these events occur every 130 years or so. This is very close to the estimated rate of explosions in supernovae.

The unexpected lack of these events, and the short continuation of the exit phase, may make them quite difficult; But, now that we know what to look for and how, astronomers will be able to build a catalog of such events. In turn, this will help us understand why they occur.

“If enough of these currents can be detected in the future, star cluster mergers may be an important mechanism for the formation of massive stars,” Zapeta said.

The study was published in Astrophysical diary letters.

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