(ORDO NEWS) — The Galactic Center is essentially the Wild West of the Milky Way.
The galaxy is dominated by a supermassive black hole with a mass 4.3 million times that of the sun, and the environment is the most hostile in the galaxy.
As we know, black holes are where stars risk certain death.
Stars that venture too close to it could turn into streams of gas and dust due to extreme tidal forces, ending what could have been a long and productive life made up of atoms.
Imagine the surprise of astronomers when they discovered the opposite – a star not dying, but being born right next to the Milky Way’s own monstrous maw, Sagittarius A* (Sgr A*).
X3a, as this new space object is known, is only a few tens of thousands of years old, just the blink of an eye by cosmic standards.
However, it is so close to Sagittarius A* that its very presence challenges our understanding of not only star formation, but also how black holes work.
Despite the dynamic intensity and powerful UV and X-ray emission that would prevent gas from merging into the star’s seed, X3a not only exists, but is in a place where a young star is not expected to form.
At 10 times the radius, 15 times the mass, and 24,000 times the mass of the Sun’s luminosity, it’s not exactly a small young star.
According to a group led by astrophysicist Florian Peisker of the University of Cologne in Germany, the reason is relatively simple.
X3a didn’t form where it is: it formed further away from the black hole and migrated inward.
“It turns out that there is a region a few light-years away from the black hole that fulfills the conditions for star formation,” Peisker explains.
“This area, a ring of gas and dust, is quite cold and protected from destructive radiation.”
The specifics of star formation are still a mystery, but we know that certain conditions must be met.
A star forms in a dense cold molecular cloud in space when the denser clump collapses, spinning under its own gravity and begins to gravitationally pull more material from the surrounding cloud.
The close proximity of a supermassive black hole is not thought to be a particularly suitable environment for such conditions.
Sgr A* is surrounded by a disk of dust and gas known as an accretion disk that spins at high speed and emits intense light.
Ultraviolet photons exert radiation pressure and photoevaporation processes that can prevent star formation, and accretion disks emit a lot of it.
Beyond a certain distance from the black hole, the material is thick enough to protect against these damaging effects and keep temperatures low enough for star formation.
According to the team’s analysis, X3a could have formed in this region, a ring of material around the galactic center.
A denser cloud could have gathered in this ring, creating enough mass in a small enough area for the gravitational collapse that triggers star formation.
This cloud started with a mass of about 100 Suns, and its gravitational collapse could have triggered the formation of several young stars.
But the X3a didn’t stay put. It began migrating towards Sgr A*, still surrounded by material as it grew.
Along the way, it could collide with other dense blocks and clouds formed in the same environment, which allowed the young star to accumulate even more mass.
Right now it is still in its growth phase, surrounded by material.
It was this clump of material, called X3, that first caught the attention of astronomers before they discovered the small star inside.
Several infrared and near-infrared instruments were able to discern the star’s long-wavelength light, which could penetrate the thick cloud shell around it.
An analysis of this glow showed that the chemical composition corresponds to a young star.
“Due to its large mass, about ten times that of the Sun, X3a is a giant among stars, and these giants are evolving very quickly towards maturity,” he says. astronomer Michal Zajacek from Masaryk University in the Czech Republic.
“We were lucky to find a massive star in the middle of a comet-shaped circumstellar envelope.
Subsequently, we identified key features associated with young age, such as how a compact circumstellar envelope orbits around it.”
The discovery of X3a could help astronomers solve another mystery that has been going on for decades.
About 20 years ago, very young stars were seen in the vicinity of Sgr A*, where it was previously thought that only very old stars could exist.
X3a suggests that the formation of young stars farther from us, and then their migration towards Sagittarius A*, may not be a particularly rare occurrence.
And this can happen not only in our galaxy. Structures around Sgr A* have been identified in many other galaxies and may contain populations of young stars of their own.
This notion could change our understanding of the dynamics of galactic nuclei.
Future work will test the star formation model not only for the Milky Way, but for the Universe as a whole.
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