What happened to the missing stars at the heart of our Milky Way galaxy?

Perhaps the supermassive black hole at the center of the Milky Way is to blame.

Observations by the Keck Observatory in Hawaii have shown that stars circling the supermassive black hole at the heart of our Milky Way galaxy are curiously lacking their binary counterparts.

Stars frequently appear in multiples. The percentage of binary star systems around our sun is 70%, which means that out of every 100 stars, 70 are part of binary star systems. This percentage is significantly greater for large stars, with practically all forming as binaries or triplets.

However, the situation is different at the galactic core of our Milky Way galaxy.

The Sagittarius A* supermassive black hole at the center of our galaxy was studied over a period of ten years by a team lead by Devin Chu of the University of California, Los Angeles. Its mass is 4.1 million times that of the sun. Within one light-month (480 billion miles or 777 billion kilometers) of the black hole, all of the stars are in orbit.

Known as "S-stars" after the black hole, sixteen of these objects are 10 times more massive than the sun and are incredibly young—less than six million years old.

Chu stated in a statement that "stars this young shouldn't even be near the black hole in the first place." Despite the fact that they couldn't have arrived in this area in less than six million years, the formation of a star in such a hostile environment is unexpected.

The team led by Chu was looking for spectroscopic binaries. Even the most advanced telescopes are occasionally unable to separate two stars in a binary system. When this occurs, the only way to tell the components apart is by examining their combined spectra and seeing a Doppler shift in the light brought on by the stars' planetary motions.

In contrast to assumptions that large stars often develop in binary or even triplet systems, Chu's team discovered that none of the S-stars are binary; instead, they are all singletons. Chu and his colleagues were able to estimate the proportion of binaries near Sagittarius A* to be 47% at most, far lower than in the region around our solar, based on their observations.

We're not dealing with a typical environment here, and this difference highlights how fascinating the environment is in the galactic core, added Chu.

What happened to their partners if these huge stars really originate as binaries? One hypothesis is that the binary systems were split by the black hole's powerful gravity, which completely ejected one of the stars from the galaxy. The population of so-called hypervelocity stars that astronomers have seen accelerating out of the galaxy at more than 1 million mph (1.6 million kph) lends credence to this concept.

Another theory is that the binary systems were sufficiently disturbed by the black hole's gravitational pull for star pairings to collide and merge. It may assist to explain why stars that appear to be so young are located in regions where it is doubtful that they could have formed if the combined star were to be rejuvenated and look much younger than it actually is.

This, according to Chu, "suggests that the black hole drives these nearby binary stars to merge or be disrupted," which has significant consequences for the creation of gravitational waves and hypervelocity stars expelled from the galactic center. The last stage, according to the scientists, is to discover how the binary percentage varies with separation from Sagittarius A*.

The new study(opens in new tab) was published last week in The Astrophysical Journal.