Baby Star Found Near Supermassive Black Hole Challenges Understanding of Star Formation
The galactic center is a highly challenging environment in the Milky Way galaxy, dominated by a supermassive black hole that is 4.3 million times heavier than the Sun.
Black holes are known to be fatal to stars that come too close, as the intense tidal forces can break them apart into streams of gas and dust, thereby preventing them from continuing their process of fusing atoms and producing energy.
It was surprising for astronomers to discover a star being born near Sagittarius A*, the supermassive black hole at the center of the Milky Way, rather than being destroyed by it.
The newly identified cosmic object, named X3a, is only a few tens of thousands of years old, which is a very short span of time on a cosmic scale. However, it is located in such close proximity to Sagittarius A* that its presence challenges our knowledge about the formation of stars and the behavior of black holes.
Despite the fact that the galactic center is characterized by intense dynamic activity and powerful radiation that would normally prevent gas from condensing and forming into a star, X3a defies expectations and exists as a newborn star in a location where none was expected to form.
X3a is not a small star, as it is 15 times more massive, 10 times larger in radius, and 24,000 times brighter than the Sun.
Astrophysicist Florian Peißker and his team from the University of Cologne in Germany believe that X3a did not form in its current location but migrated towards the black hole from a further distance.
Peißker explains that a ring of gas and dust, located a few light years away from the black hole, provided the necessary conditions for star formation. This region is cold and shielded from destructive radiation.
Although the exact process of star formation is not yet fully understood, it is known that it occurs within a dense, cold molecular cloud in space. A dense clump within the cloud collapses under its own gravity and starts to attract more material from the surrounding cloud, causing it to spin and eventually form a star.
The immediate vicinity of a supermassive black hole is not considered conducive to the conditions necessary for star formation. Sgr A* is surrounded by an accretion disk, which is a disk of gas and dust swirling around the black hole at high speeds and emitting intense light. The radiation from ultraviolet photons can hamper star formation by exerting radiation pressure and photoevaporation processes, and accretion disks emit a lot of this radiation.
However, beyond a certain distance from the black hole, the material is thick enough to protect against these destructive influences and keep temperatures cool enough for star formation to occur.
The team’s analysis suggests that X3a could have formed in a ring of material around the galactic center. In this region, a denser cloud of material could have come together, generating enough mass in a small area for the gravitational collapse that initiates the star formation process.
This cloud began with a mass of about 100 Suns and could have triggered the formation of multiple baby stars through its gravitational collapse.
Nevertheless, X3a didn’t stay in place. It started moving towards Sgr A* while still surrounded by material, allowing it to grow in mass. On its journey, it may have come across other dense clumps and clouds that formed in the same environment, further contributing to its growth. Currently, the star is still in its growth phase, surrounded by material.
Galactic center, dominated by an enormous supermassive black hole 4.3 million times more massive than the Sun, is the most inhospitable environment in the galaxy. It’s where stars venture too close to black holes, risking certain death. Astronomers were surprised to find X3a, a young star located near the Milky Way’s monstrous maw Sagittarius A* (Sgr A*), which is just a few tens of thousands of years old. It sits so close to Sgr A* that its very presence challenges our understanding of not just star formation but the operations of black holes. At 10 times the radius, 15 times the mass, and 24,000 times the luminosity of the Sun, it’s not exactly a petite infant star either.
Astrophysicist Florian Peißker of the University of Cologne in Germany led a team that investigated the formation of X3a. According to the team, the immediate vicinity of a supermassive black hole is not a good environment for star formation. Ultraviolet photons exert radiation pressure and photoevaporation processes, curtail star formation, and accretion disks emit a lot of destructive radiation. But the team’s analysis suggests that X3a could have formed in a region at a distance of a few light years from the black hole, a ring of material around the galactic center. In this ring, a denser cloud could have come together, generating enough mass in a small enough area for the gravitational collapse that starts the star formation process.
X3a could have migrated inward toward Sgr A* while surrounded by material, allowing it to grow in size by encountering other dense clumps and clouds that formed in the same environment. It’s still surrounded by material and in the growth phase now. X3a’s discovery could help astronomers understand the formation of young stars farther out, followed by their migration in towards Sgr A*. Previously, it was thought that only very old stars could exist in the vicinity of Sgr A*, but X3a suggests that the formation of young stars farther out followed by their migration towards Sgr A* might be more common than previously thought.
X3a was discovered as a blob of material, named X3, before the baby star inside it was identified. Multiple infrared and near-infrared instruments could discern the long-wavelength light of the star that could penetrate the thick cloud envelope around it. Analysis of this light revealed chemistry consistent with a baby star. Astronomer Michal Zajaček at Masaryk University in Czechia said, “With its high mass of about ten times the solar mass, X3a is a giant among stars, and these giants evolve very quickly towards maturity. We have been lucky to spot the massive star in the midst of the comet-shaped circumstellar envelope. Subsequently, we identified key features associated with a young age, such as the compact circumstellar envelope rotating around it.”
The center of the Milky Way, known as the galactic center, is considered to be the most dangerous place in the galaxy. It is dominated by a supermassive black hole that is 4.3 million times the mass of the Sun. Black holes are known to be deadly to stars, which can be torn apart by tidal forces when they get too close. However, a new star called X3a has been discovered near the galactic center that challenges our understanding of star formation and black hole operations. X3a is just a few tens of thousands of years old and sits very close to Sagittarius A*, the supermassive black hole.
X3a is 15 times more massive than the Sun and 10 times larger in radius. The team led by Florian Peißker of the University of Cologne discovered that X3a did not form where it currently resides; instead, it migrated inwards from a few light years away from the black hole. There is a region around the black hole that is shielded against destructive radiation and cold enough for star formation. A denser cloud in this region collapsed under its own gravity, forming a star. This cloud had a mass of about 100 Suns, and its gravitational collapse could have triggered the formation of several baby stars. X3a started migrating towards Sgr A*, accumulating more mass as it encountered other dense clumps and clouds in its path.
The discovery of X3a suggests that the formation of young stars followed by their migration towards supermassive black holes might not be an uncommon occurrence. This discovery could help resolve a mystery surrounding the presence of very young stars near Sgr A* that were observed around 20 years ago. The structures around Sgr A* have also been observed in many other galaxies, and they could potentially host populations of baby stars. This notion could change our understanding of the dynamics of galactic nuclei. Further studies will be carried out to test the star formation model proposed by the team, not just for the Milky Way but for the broader Universe.
The research has been published in The Astrophysical Journal Letters.