A stellar dust factory

STRIKING NEW OBSERVATIONS with the Atacama Large Millimetre/submillimetre Array (ALMA) telescope capture, for the first time, the remains of a recent supernova brimming with freshly formed dust. If enough of this dust makes the perilous transition into interstellar space, it could explain how many galaxies acquired their dusty, dusky appearance.

Cosmic dust consists of silicate and graphite grains – minerals also abundant on Earth. The soot from a candle is very similar to cosmic graphite dust, although the size of the grains in the soot are ten or more times bigger than typical grain sizes of cosmic graphite grains.

This image shows the remnant of Supernova 1987A

This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the middle of the remnant. Hubble Space Telescope (in green) and Chandra Space Observatory (in blue) data show the expanding shock wave. Credit: ALMA (ESO/NAOJ/NRAO) / A. Angelich. Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory

Galaxies can be remarkably dusty places and supernovae – exploded stars – are thought to be a primary source of that dust, especially in the early universe. But direct evidence of a supernova’s dust-making capabilities has been slim up to now, and could not account for the copious amount of dust detected in young, distant galaxies. But now observations with ALMA are changing that.

An international team of astronomers used ALMA to observe the glowing remains of Supernova 1987A, which is in the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way about 160,000 light-years from Earth. SN 1987A is the closest observed supernova explosion since Johannes Kepler’s observation of a supernova inside the Milky Way in 1604. Being far in the southern sky, it is clearly visible only from the Southern Hemisphere.

The Tarantula Nebula and its surroundings

This is an image of the Tarantula Nebula and its surroundings in the Large Magellanic Cloud galaxy, taken in 1987. Supernova 1987A is the bright star just to the right of centre. Credit: ESO

“This is the first time we’ve been able to really image where the dust has formed, which is important in understanding the evolution of galaxies,” said Remy Indebetouw, an astronomer at the National Radio Astronomy Observatory (NRAO) and the University of Virginia, both in Charlottesville, USA

Astronomers predicted that as the gas cooled after the explosion, large amounts of dust would form as atoms of oxygen, carbon, and silicon bonded together in the cold central regions of the remnant. However, earlier observations of SN 1987A with infrared telescopes, made during the first 500 days after the explosion, detected only a small amount of hot dust.

With ALMA’s resolution and sensitivity, the team was able to image the far more abundant cold dust, which glows brightly in millimetre and submillimetre light. The astronomers estimate that the remnant cloud now contains about 25 percent the mass of the Sun in newly formed dust. They also found that significant amounts of carbon monoxide and silicon monoxide have formed.

Aerial view of dishes of the Atacama Large Millimetre/submillimetre Array

Aerial view of dishes of the Atacama Large Millimetre/submillimetre Array (ALMA) telescope. Credit: ALMA

“SN 1987A is a special place since it hasn’t mixed with the surrounding environment, so what we see there was made there,” said Indebetouw. “The new ALMA results, which are the first of their kind, reveal a supernova remnant chock full of material that simply did not exist a few decades ago.”

There’s more information on Supernova 1987A, including an interview with Australian astronomers, on the ABC’s web site.

Adapted from information issued by NRAO.

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