Wednesday , March 3 2021

Astronomers mapped the stunning accelerating outflows of the stellar explosion

In the star-forming cloud, material has been found that accelerates outside the stellar explosion site.

It’s only the second time such outflows of molecules have ever been clearly seen, but it could help astronomers understand how the most massive stars originate in life.

In the 1980s, astronomers discovered something special in the Orion nebula that formed stars: a stream of dense molecular gas that travels at speed through space. When these stream graves were mapped, they appeared to originate from a single point.

Since then, molecular currents have been observed in many star-forming regions. They are believed to play an important role in the formation of low-mass stars, carrying away an extra angular momentum that would otherwise make baby stars rotate into oblivion.

However, the outflow of Orion was unique. Molecular flows in low-mass stars are bidirectional; in other words, there are only two of them, shooting in opposite directions. There were many more Orion outflows … and they were also found in an area where much more massive stars form – more than 10 times the mass of the Sun.

w28Combined X-ray, radio, and optical image of W28, the base complex of the region. (NASA / ROSAT; NOAO / CTIO / PF Winkler et al; NSF / NRAO / VLA / G. Dubner et al.)

Now we don’t know as much about the formation of massive stars as we do about smaller ones. Massive star nurseries are rarer and usually farther away, making them harder to see. So astronomers thought that perhaps the outflows of Orion could produce clues.

However, there was nothing at the source of the leaks – not massive baby stars. This can mean several explosive scenarios, such as the merging of two massive baby stars or the gravitational energy released from the formation of a nearby massive binary. But based on just one kind of observation, it is difficult to make a firm decision.

To try and learn more about this phenomenon, a team of astronomers led by Luis Zapata of the National Autonomous University of Mexico decided to translate one of our most powerful radio telescopes, the Atacama Large Millimeter / submillimeter Array (ALMA), in a known massive region. star nursery.

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

G5.89−0.39, also known as W28 A2, is about 9752 light-years away. It contains a bright, expanding shell-like ultra-compact hydrogen cloud and strong molecular currents. Zapata and his team had previously pointed out that six of these filaments appeared to point directly into the middle of the hydrogen cloud, but their results were not convincing.

ALMA cleared this ambiguity immediately. It detected dense current conductors based on millimeter wavelengths of carbon dioxide and silica.

outflows(Zapata et al., ApJL, 2020)

Astronomers were able to identify 34 molecular beams that zoomed radially away from the heart of the cloud and accelerated outward. Based on their speed of up to 130 kilometers per second, the outflows are about 1,000 years old; what the explosion produced them happened about a thousand years ago.

They’re not as powerful as you’d expect from a supernova explosion that happens when a massive star dies. In addition, as was seen in the case of Orion, there were no stars in the middle – only an area of ​​ionized gas, possibly as a result of heating during the explosion event.

If the event was associated with a star (or multiple stars) that produced outflows, it could have been removed from the area.

Because massive stars always form as clusters, such interactions are potentially quite common, which in turn may shed some light on star formation. If the two protostars merged, they would probably have ended up as one much larger star.

Based on Orion’s outflows, G5.89 outflows, and marginal detection, which could be a similar outflow in the star-forming region known as DR-21, the team estimates that these events occur approximately every 130 years. It is very close to the estimated number of supernova explosions.

The unpredictability of these events and the short duration of the outflow phase may make them quite difficult to find; but now that we know what we are looking for and how, astronomers may be able to build a list of such events. That in turn helps us understand why they occur.

“If enough of these outflows can be observed in the future, merging star clusters could be an important mechanism for the formation of massive stars,” Zapata said.

The study has been published The Astrophysical Journal Letters.

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