Japanese astronomers have captured images of an astonishing 1800 supernovae. 58 of these supernovae are the scientifically-important Type 1a supernovae located 8 billion light years away. Type 1a supernovae are known as ‘standard candles’ in astronomy.
The team of astronomers used the Subaru Telescope and one of the world’s most powerful digital cameras to find these supernovae. The astronomers come from the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), Tohoku University, Konan University, the National Astronomical Observatory of Japan, and other institutions. The team was led by Professor Naoki Yasuda of the IPMU, and their results were published online at Publications of the Astronomical Society of Japan.
A supernova is a star that has reached the end of its life and exploded brilliantly. Supernovae brighten the sky for up to six months, and can outshine their host galaxy. These type 1a supernovae, or standard candles, are particularly useful because of their steady light. Since their light doesn’t fluctuate much, they are ideal for accurately measuring their distance from Earth. Standard candles are used to measure the expansion rate of the universe.
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Even though the team found 1800 supernovae, of which 58 were standard candles, they were actually looking for something more elusive.
In recent years astronomers have reported another type of supernova even brighter than Type 1a. These are called Super Luminous Supernovae because they’re so bright. They can be up to 10 times brighter than other supernovae, and their extreme brightness allows astronomers to spot them at extreme distances.
This is important, because when astronomers look at objects in the extreme distant universe, they’re seeing the light that left them billions of years ago. So in that way, astronomers are looking back in time to the early days of the universe. They can look back at the conditions in the early universe that allowed these first, massive stars to form.
Even though this survey found 1800 supernovae, they are still rare events. And there are only a handful of telescopes that can capture sharp images of them. This effort by the Japanese team used one of those ‘scopes, the Subaru Telescope, and combined it with one of the world’s best digital cameras to find these supernovae.
The camera is the Hyper Suprime-Cam (HSC). It’s a gigantic camera larger than a human and it’s attached to the 8.2 meter Subaru Telescope at Maunakea Hawaii. The Hyper Suprime-Cam boasts a whopping 870 megapixels.
Over a six month period, Professor Yasuda and his team took repeated images of the same areas of the night sky. By looking for stars that appeared suddenly brighter before fading out, they were able to identify the supernovae.
Overall, the team found 1800 supernovae, an astonishing number. (Compare that to the Hubble Space Telescope, which took 10 years to discover 50 supernovae greater than 8 billion light years from Earth.) Of those, 400 were the desirable Type 1a supernovae, with 58 of them over 8 billion light years from Earth. Even more remarkable, they identified 5 super luminous supernovae.
“The Subaru Telescope and Hyper Suprime-Cam have already helped researchers create a 3D map of dark matter, and observation of primordial black holes, but now this result proves that this instrument has a very high capability finding supernovae very, very far away from Earth. I want to thank all of my collaborators for their time and effort, and look forward to analyzing our data to see what kind of picture of the Universe it holds,” said Yasuda.
Determining the expansion rate of the universe is one of the over-arching goals in astronomy and cosmology. The supernova data from this study will help astronomers refine their estimate of that rate, and will also help them understand dark energy, the mysterious force that drives the expansion.