NASA / Swift / Stefan Immler
Credit: Fox / Cucchiara / Levan / Tanvir
Some information about Gamma-ray bursts
written by Derek Fox, the mission scientist for the proposed JANUS observatory
Gamma-ray bursts like GRB 090429B are convincingly explained as originating with the death of a massive, short-lived star, 30 or more times the mass of our Sun, when exhaustion of the nuclear fuel in its core regions causes the core to collapse into a black hole. As the newly-formed black hole consumes gas from the star’s outer layers, it emits two powerful jets that erupt from the star’s surface, accelerate to speeds very near the speed of light, and power a beamed and highly-luminous burst of high-energy emission — the gamma-ray burst.
At an estimated distance of 13.14 billion light years, GRB 090429B exploded when the universe was less than 4% of its present age, just 520 million years old, and less than 10% of its present size. Astronomers argue that the very first stars and galaxies could not possibly have formed more than 400 million years prior to this, and so the galaxy hosting the progenitor star of GRB 090429B was truly one of the first galaxies in the universe. Beyond the possible cosmic distance record, then, demonstration of this burst as a possible record-breaker illustrates how gamma-ray bursts can be used to reveal the locations of massive stars in the early universe and to track the processes of the formation of galaxies and stars, which eventually led to the galaxy-rich cosmos we see around us today.
With better luck, or more-advanced facilities, it should be possible in the future to use the bright afterglows of bursts like GRB 090423 and GRB 090429B to explore the conditions of star and galaxy formation at these early cosmic epochs in detail. NASA’s forthcoming James Webb Space Telescope, due to launch in 2017, has been carefully engineered for studies of the early universe, and an afterglow spectrum from this facility would be a unique and valuable source of data for understanding the first galaxies and the various processes guiding their formation.
Making discovery and exploitation of the most-distant bursts significantly more efficient likely will require a next-generation mission. To this end, Penn State has partnered with the Southwest Research Institute, Cornell University, and other institutions to propose the JANUS explorer to NASA, with a target launch date in early 2017. By discovering and observing the most-distant gamma-ray bursts and quasars, and by measuring their distances autonomously without the need for follow-up observations, JANUS would provide a steady stream of rewarding targets to James Webb and ground-based telescopes. The most exciting prospect, according to Fox, is to imagine JANUS and James Webb working together in space. Nothing else illuminates conditions in the early universe like its “brightest lights,” the gamma-ray bursts and quasars.