Near the crowded galactic center, where billowing clouds of gas and dust cloak a supermassive black hole three million times as massive as the sun—a black hole whose gravity is strong enough to grip stars that are whipping around it at thousands of kilometers per second—one particular cloud has baffled astronomers. Indeed, the cloud, dubbed G0.253+0.016, defies the rules of star formation.
In infrared images of the galactic center, the cloud—which is 30 light-years long—appears as a bean-shaped silhouette against a bright backdrop of dust and gas glowing in infrared light. The cloud's darkness means it is dense enough to block light.
According to conventional wisdom, clouds of gas that are this dense should clump up to create pockets of even denser material that collapse due to their own gravity and eventually form stars. One such gaseous region famed for its prodigious star formation is the Orion Nebula. And yet, although the galactic-center cloud is 25 times denser than Orion, only a few stars are being born there—and even then, they are small. In fact, the Caltech astronomers say, its star-formation rate is 45 times lower than what astronomers might expect from such a dense cloud.
To determine whether the cloud contained clumps of denser gas, called dense cores, the team used the Submillimeter Array (SMA), a collection of eight radio telescopes on top of Mauna Kea in Hawaii. In one possible scenario, the cloud does contain these dense cores, which are roughly 10 times denser than the rest of the cloud, but strong magnetic fields or turbulence in the cloud disturbs them, thus preventing them from turning into full-fledged stars.
Next, the astronomers wanted to see if the cloud is being held together by its own gravity—or if it is swirling so fast that it is on the verge of flying apart. If it is churning too fast, it can't form stars. Using the Combined Array for Research in Millimeter-wave Astronomy (CARMA)—a collection of 23 radio telescopes in eastern California run by a consortium of institutions, of which Caltech is a member—the astronomers measured the velocities of the gas in the cloud and found that it is up to 10 times faster than is normally seen in similar clouds. This particular cloud, the astronomers found, was barely held together by its own gravity. In fact, it may soon fly apart.
Learn more about it here, courtesy of CalTech.