National Astronomical Observatory of Japan

Gigantic Explosion Buried in Dust: ALMA Probes Environment around Gamma Ray Bursts

| Science

For the first time, a group of Japanese researchers detected radio emission from molecular gas in galaxies hosting gamma ray bursts (GRBs), the brightest explosive phenomenon in the universe, with the Atacama Large Millimeter/submillimeter Array (ALMA). Also, this observation revealed that the observed GRBs occurred in a remarkably dust-rich environment with little molecular gas.

The research group led by the Chile Observatory of the National Astronomical Observatory of Japan (NAOJ) conducted observations of two galaxies hosting GRB 020819B and GRB 051022 whose distance from us is about 4.3 billion and 6.9 billion light years, respectively. Detection of radio emission from GRB host galaxies, which had been a long-sought goal for astronomers, was finally made possible by ALMA with its unprecedentedly high sensitivity.

On top of this, ALMA’s unparalleled high resolution (eyesight) also revealed that the GRB 020819B host is very different in its spatial distribution of molecular gas and dust; molecular gas is distributed at the nuclear region while dust is concentrated at the GRB explosion site. The ratio of dust to molecular gas at the GRB site is ten or more times higher than other normal environments. It is the first time that the spatial distribution of molecular gas and dust in the GRB host galaxies was verified by observations.

Radio intensity distributions of molecular gas (left) and dust (middle), both of which were observed with ALMA. An optical image captured by the Frederick C. Gillett Gemini North telescope (right). The cross mark in the upper center shows the location of the GRB site. Credit: Bunyo Hatsukade (NAOJ)/ALMA (ESO/NAOJ/NRAO)/Gemini Observatory

The scientific paper on which this article is based appears in the Nature published on June 12, 2014.


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