The centre of our galaxy is home to a strange cohort of stars that should never have existed, and we may now know how they formed. The gravity in this area, next to the supermassive black hole at the middle of the Milky Way, is so powerful that it should disrupt any clouds dense enough to begin turning into stars, but the shock wave from another star’s violent demise could have given those nascent stars a window of opportunity.
Most ideas to explain the existence of more than 100 young stars within a few light years of the Milky Way’s centre involve the stars forming elsewhere and then migrating inwards. But if that were the case, we would expect the stars to orbit within the disc of the galaxy, not misaligned from it as they appear to be.
at Stony Brook University in New York and at Monash University in Australia have come up with a different idea for how these unexpected stars may have formed. When a star wanders too close to a black hole, that star is ripped apart in what’s called a tidal disruption event (TDE). These events cause huge explosions and sometimes enormous jets with shock waves that propagate through the surrounding dust and gas.
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When the researchers calculated how one of these shock waves would affect the clouds of gas near the galactic centre, they found that it would compress the gas enough for it to hold together in the region’s intense gravity. After the shock wave compressed the gas by a factor of tens or even hundreds of millions, it would only be a matter of time before those clumps started to become stars, says Perna.
“We know that explosive events have a feedback effect on star formation in other contexts,” she says. “As we were looking into the details of it here, all the numbers in terms of rates, energetics, length scales, they all just fell into place.”
The expected rate of TDEs with jets near the galactic centre – about one every few million years – is similar to the age of these stars. Plus, the shock waves would not necessarily be aligned with the disc of the galaxy, so it makes sense that the stars would form outside of the galactic disc. The expected masses of the stars formed via this mechanism line up with the measured masses of the stars in this region, as well. Detailed simulations should help researchers determine whether the strange stars at the centre of our galaxy really do come from the shredding of less lucky stars, Perna says.
The Astrophysical Journal Letters
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