NASA's Hubble Space Telescope has recently delivered the strongest evidence yet that short-duration gamma
ray bursts are produced by the merger of two small, super-dense stellar objects.
The evidence is in the detection of a new kind of stellar blast called a kilonova, which results from the
energy released when a pair of compact objects crash together.
Hubble observed the fading fireball from a kilonova last month, following a short gamma ray burst (GRB)
in a galaxy almost 4 billion light-years from Earth.
Click on image to enlarge
These images taken by NASA's Hubble Space Telescope reveal a new type of stellar explosion produced from the merger of two compact objects.
Hubble spotted the outburst while looking at the aftermath of a short- duration gamma-ray burst, a mysterious flash of intense high-energy radiation that appears from random directions in space. Short-duration blasts last at most a few seconds. They sometimes, however, produce faint afterglows in visible and near-infrared light that continue for several hours or days and help astronomers pinpoint the exact location of the burst.
In the image at left, the galaxy in the center produced the gamma-ray burst, designated GRB 130603B. The galaxy, cataloged as SDS J112848.22+170418.5, resides almost 4 billion light-years away. A probe of the galaxy with Hubble's Wide Field Camera 3 on June 13, 2013, revealed a glow in near-infrared light at the source of the gamma-ray burst, shown in the image at top, right. When Hubble observed the same location on July 3, the source had faded, shown in
the image at below, right. The fading glow provided key evidence that it was the decaying fireball of a new type of stellar blast called a kilonova.
Credit: NASA, ESA, N. Tanvir (University of Leicester), A. Fruchter (STScI), and A. Levan (University of Warwick)
A kilonova had been predicted to accompany a short-duration GRB, but had not been seen before.
"This observation finally solves the mystery of the origin of short gamma ray bursts," said Nial Tanvir of
the University of Leicester, UK who led a team studying the recent
"Many astronomers, including our group, have already provided a great deal of evidence that long-duration
gamma ray bursts (those lasting more than two seconds) are produced by the collapse of extremely massive stars."
But we only had weak circumstantial evidence that short bursts were produced by the merger of compact objects.
This result now appears to provide definitive proof supporting that scenario."
A kilonova is about 1,000 times brighter than a nova, which is caused by the eruption of a white dwarf.
The self-detonation of a massive star, a supernova, can be as much as 100 times brighter than a kilonova.
Gamma ray bursts are mysterious flashes of intense high-energy radiation that appear from random directions in space.
Short-duration blasts last at most a few seconds, but they sometimes produce faint afterglows in visible
and near-infrared light that continue for several hours or days.
Click on image to enlarge
A pair of neutron stars in a binary system spiral together. Orbital momentum is dissipated through the release of gravity waves, which are tiny ripples in the fabric of space-time.
In the final milliseconds, as the two objects merge, they kick out highly radioactive material. This material heats up and expands, emitting a burst of light called a kilonova. An accompanying gamma-ray burst lasts just one-tenth of a second, but is 100 billion times brighter than the kilonova flash.
The fading fireball blocks visible light but radiates in infrared light.
A remnant disk of debris surrounds the merged object, which may have collapsed to form a black hole. Credit: NASA, ESA, and A. Field (STScI)
The afterglows have helped astronomers determine that GRBs lie in distant galaxies.
Astrophysicists have predicted short-duration GRBs are created when a pair of super-dense neutron stars in
a binary system spiral together.
This event happens as the system emits gravitational radiation, creating tiny waves in the fabric of
space-time. The energy dissipated by the waves causes the two stars to sweep closer together.
In the final milliseconds before the explosion, the two stars merge into a death spiral that kicks out highly
This material heats up and expands, emitting a burst of light.