A Star is Born
“The properties of star formation are well defined and require environments characterized by a sufficiently low temperature (less than 20 K) and a high gas density,” said lead author Dr. Florian Peißker from the I. Physikalisches Institut der Universität zu Köln und colleagues.
“In contrast, the temperature of gaseous-dusty filaments in the center of our Milky Way Galaxy exceeds a gas temperature of 6,000 K and a dust temperature of 250 K.”
“Furthermore, the velocity dispersion of all known objects close to Sagittarius A*, the 4-million-solar-mass black hole at the Galactic center, outpaces typical numerical values in star formation regions by several magnitudes.”
“Due to the presence of Sagittarius A*, tidal forces hinder gas clumping, which is necessary for the formation of stars.”
In the research, the astronomers used almost 30 years of data from four different telescopes to study a highly dynamic stellar object close to Sagittarius A*.
They found that the object, dubbed X3a, has an age of a few 10,000 years, is 10 times as big and 15 times as heavy as our Sun, and likely belongs to a star cluster called IRS 13.
“It turns out that there is a region at a distance of a few light-years from the black hole which fulfils the conditions for star formation,” Dr. Peißker said.
“This region, a ring of gas and dust, is sufficiently cold and shielded against destructive radiation.”
“Low temperatures and high densities create an environment in which clouds of hundreds of solar masses can form.”
“These clouds can in principle move very fast towards the direction of the black hole due to cloud-cloud collisions and scattering that remove the angular momentum.”
“In addition, very hot clumps formed in close proximity to the baby star which could then be accreted by X3a.”
“These clumps could thus also contribute to X3a reaching such a high mass in the first place.”
“However, these clumps are only a part of the formation history of X3a. They still do not explain its birth.”
“We assume the following scenario to be possible: shielded from the gravitational influence of Sagittarius A* and intense radiation, a dense enough cloud could have formed in the outer gas and dust ring around the center of the Galaxy.”
“This cloud had a mass of about 100 solar masses and collapsed under its own gravity to one or more protostars.”
“This so-called fall time approximately corresponds to the age of X3a.”
“With its high mass of about 10 solar masses, X3a is a giant among stars, and these giants evolve very quickly towards maturity,” said co-author Dr. Michal Zajaček, an astronomer at Masaryk University.
“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.”
A paper describing the findings was published in the Astrophysical Journal.
Florian Peißker et al. 2023. X3: A High-mass Young Stellar Object Close to the Supermassive Black Hole Sgr A*. ApJ 944, 231; doi: 10.3847/1538-4357/aca977