Wednesday, July 15, 2015

Birth of a Supermassive Black Hole

The existence of supermassive black holes (SMBHs) with ~1 billion times the Sun’s mass in the early Universe is a puzzle because there is insufficient time for stellar mass black holes with ~10 times the Sun’s mass to grow into SMBHs. A study by Matsumoto et al. (2015) propose that the conditions present in the early Universe can allow protostars to quickly grow to form supermassive stars (SMSs) with ~100,000 times the Sun’s mass. When these SMSs exhaust their nuclear fuel, they collapse directly to form massive black holes with ~10,000 times the Sun’s mass. These massive black holes can seed the formation of SMBHs in the early Universe.

A SMS is expected to have a radius of roughly 1 billion kilometres and a lifespan of only ~1 million years. Once the SMS exhausts its nuclear fuel, it starts collapsing into a massive black hole. During the collapse, relativistic jets can be launched from the accretion disk around the growing, nascent black hole. The relativistic jets can break through the star’s surface to produce an ultra-long gamma ray burst (ULGRB) with duration of ~10,000 to 1,000,000 seconds. Gamma-ray bursts (GRBs) are generally classified into short gamma-ray bursts (SGRBs) with durations under 2 seconds and long gamma-ray bursts (LGRBs) with duration greater than 2 seconds. ULGRBs are a third class of GRBs with durations of ~10,000 seconds or more. The collapse of SMSs into massive black holes may be observed as ULGRBs.

Matsumoto et al. (2015), “Direct Collapse Black Holes Can Launch Gamma-Ray Bursts and Get Fat to Supermassive Black Holes?”, arXiv:1506.05802 [astro-ph.HE]