By observing two neighboring galaxies, the Large Magellanic Cloud and the Small Magellanic Cloud, using the Murchison Widefield Array radio telescope in Australia, astronomers have detected cosmic rays and hot gas and identified patches where new stars are born and remnants from stellar explosions can be found.
A red, green, blue composite image of the Large Magellanic Cloud made from radio wavelength observations at 123, 181 and 227 MHz. At these wavelengths, emission from cosmic rays and the hot gases belonging to the star forming regions and supernova remnants of the galaxy are visible. Image credit: International Centre for Radio Astronomy Research.
Cosmic rays are very energetic charged particles that interact with magnetic fields to create radiation we can see with radio telescopes.
“These rays actually originate in supernova remnants — remnants from stars that exploded a long time ago,” said Professor Lister Staveley-Smith, an astrophysicist at the International Centre for Radio Astronomy Research.
“The supernova explosions they come from are related to very massive stars, much more massive than our own Sun.”
“The number of cosmic rays that are produced depends on the rate of formation of these massive stars millions of years ago.”
The Large and Small Magellanic Clouds are very close to our own Milky Way Galaxy — less than 200,000 light-years away — and can be seen in the night sky with the naked eye.
A red, green, blue composite image of the Small Magellanic Cloud made from radio wavelength observations taken at 123, 181 and 227 MHz. Image credit: International Centre for Radio Astronomy Research.
“This was the first time the galaxies had been mapped in detail at such low radio frequencies,” said Dr. Bi-Qing For, an astronomer at the International Centre for Radio Astronomy Research.
“Observing the Magellanic Clouds at these very low frequencies — between 76 and 227 MHz — meant we could estimate the number of new stars being formed in these galaxies.”
“We found that the rate of star formation in the Large Magellanic Cloud is roughly equivalent to one new star the mass of our Sun being produced every ten years,” she said.
“In the Small Magellanic Cloud, the rate of star formation is roughly equivalent to one new star the mass of our Sun every forty years.”
Included in the observations are the massive star-forming region 30 Doradus (also known the Tarantula Nebula) and the remnant of core-collapse Supernova 1987A, both are in the Large Magellanic Cloud.
“Our results are an exciting glimpse into the science that will be possible with next-generation radio telescopes,” Professor Staveley-Smith said.
“It shows an indication of the results that we will see with the upgraded Murchison Widefield Array, which now has twice the previous resolution.”
The findings appear in the journal Monthly Notices of the Royal Astronomical Society.
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B-Q For et al. 2018. A multifrequency radio continuum study of the Magellanic Clouds – I. Overall structure and star formation rates. MNRAS 480 (2): 2743-2756; doi: 10.1093/mnras/sty1960
