Astronomers have finally found evidence of dust around a relatively “old” supernova remnant near the centre of our Milky Way galaxy. This new finding can help explain the mystery of how galaxies in the early Universe, only a few billion years after the Big Bang, can contain so much dust.
The main elements from which interstellar dust is made – carbon, silicon, magnesium and iron – are all made inside stars and expelled into the interstellar medium when stars die. This dust is then recycled in the next generation of stars (and some of it goes into forming planets like the Earth).
But stars like our own Sun, with lifetimes of about 10 billion years, live too long to be able to account for the vast amounts of dust in the early Universe. Astronomers have long believed the answer to this riddle lies in supernovae explosions that result when massive stars die. The accelerated timescales on which these explosions take place can potentially explain the early dust content in the Universe.
There is one problem with this idea—supernovae explosions are some of the most energetic events in our Universe. A single supernova can briefly outshine an entire galaxy! While these conditions are necessary to fuse the heaviest elements in the Universe, supernova explosions and their resulting supernova remnants are very violent environments and it was unclear whether dust grains could survive the shocks and reverse shocks that reverberate in the surrounding medium.
In July of last year, researchers published new results from the Very Large Telescope which observed dust formation in real-time over a 2.5-year period following the explosion of supernova SN2010jl. Their observations showed that an accelerated dust formation process begins just a few hundred days after the explosion, producing grains as large as 1 micron in size—large enough to be resistant to destruction. These larger grains should still be observable after many years.
Using the mid-infrared camera on the Stratospheric Observatory for Infrared Astronomy (SOFIA), a modified Boeing 747 that flies at an elevation of 12 km, Ryan Lau of Cornell University and collaborators found an “old” supernova remnant, Sagittarius A East, near the Galactic center which contains about 6,700 Earth-masses of warm (~100 K) dust. Sagittarius A East is about 10,000 years old which means that the dust has survived the destructive shocks and reverse shocks created from the initial supernova explosion.
The results of Lau et al. supports the theory that galaxies in the early Universe can indeed be enriched with dust by supernovae, which could solve the long-standing mystery.
For more information, see
- Milky Way’s center unveils supernova ‘dust factory’, Science Daily
- NASA’s SOFIA Finds Missing Link Between Supernovae and Planet Formation, NASA press release, 19 March 2015
- Old supernova dust factory revealed at the Galactic center, Lau et al. (2015), Science, 19 March 2015
- VLT Clears Up Dusty Mystery, ESO Science Release, 9 July 2014
[Mark Hutchison & Sarah Maddison]