The Galactic Center is basically the Wild West of the Milky Way. It is dominated by a supermassive black hole with a mass of 4.3 million times that of the Sun, and is considered the most hostile environment in the galaxy.
Black holes, as we know, are places where stars run the risk of dying. Stars that venture too close to one can be reduced to a stream of gas and dust by intense tidal forces, ending the long and fruitful life of atomic coalescing.
Imagine the surprise of astronomers when they discovered its opposite – a star that did not die but was in the process of being born near the terrifying Milky Way, Sagittarius A* (Sgr A*).
X3a, as this new cosmic body is known, is only a few tens of thousands of years old, and barely spread out in cosmic time. However, it is so close to Sgr A* that its presence challenges our understanding not only of star formation but also of black hole processes.
Although its dynamic density and strong ultraviolet radiation and X-rays prevent gas from fusing into the stellar seed, X3a is not only absent but is located where young stars are not expected to form.
At 10 times its radius, 15 times its mass, and 24,000 times the luminosity of the Sun, it’s not a small star either.
According to a team led by astrophysicist Florian Becker of the University of Cologne in Germany, the reason is relatively simple. X3a didn’t form in its place: it formed far from the black hole and migrated inward.
“It turns out that there is a region a few light years from the black hole that meets the conditions for star formation,” Peißker explained. “This region, the ring of gas and dust, is quite cold and protected from damaging radiation.”
The details of star formation are still unclear, but we know that certain conditions must be met. A star forms in a dense, cold molecular cloud in space, when the denser mass collapses and rotates under its own gravity and begins to gravitationally pull more matter out of the surrounding cloud.
The environment around a supermassive black hole is not a very good environment for these conditions. Sgr A* is surrounded by a disk of dust and gas known as an accretion disk, which rotates around it at high speed and emits intense light. UV photons exert radiation pressure and the process of photoevaporation can Reduces star formation And the accumulator disc radiates a lot.
After a certain distance from the black hole, the material is thick enough to protect against these damaging effects and keeps temperatures cool enough to form stars.
According to the team’s analysis, X3a could have formed in this region, a ring of material around the center of the galaxy. In these rings, denser clouds can agglomerate, creating enough mass in a small enough region for the gravitational collapse that initiates the star formation process.
This cloud starts with the mass of about 100 suns, and its gravitational collapse will result in the formation of many young stars.
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But the X3a doesn’t stand still. It started migrating to Sgr A*, still surrounded by material as it grew. On your way, you may find other dense clumps and clouds that form in the same environment, allowing the young star to gather more mass. It’s still in its infancy, surrounded by matter.
It was this clump of matter, called X3, that first caught astronomers’ attention, before they recognized the tiny star inside. Several infrared and near-infrared instruments can distinguish the long-wavelength light from a star that can penetrate the dense surrounding cloud cover. Analysis of this light reveals consistent chemistry with the baby stars.
“With a high mass of about ten times that of the Sun, X3a is an interstellar giant, and this giant is growing very quickly towards maturity,” says astronomer Michel Zajec at Masaryk University in the Czech Republic.
“We were fortunate to have detected a massive star in the center of a comet-shaped casing. Next, we identify key features associated with youth, such as the young stellar shroud orbiting it.”
X3a’s discovery could help astronomers solve another decades-old mystery. About 20 years ago, very young stars were observed near Sgr A*, where only very old stars were previously thought. X3a suggests that distant young stars, followed by their migration towards Sgr A*, may not be such an unusual event.
And it may not only happen in our galaxy. Structures around Sgr A* have been identified in many other galaxies, and they may host their own young star clusters. It’s an idea that could change our understanding of galactic core dynamics.
Future work will test the team’s model of star formation, not just for the Milky Way but for the wider universe.
Research published in Astrophysics Journal Letter.
