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Wednesday, 3 June 2020
Supernova 1994D: The image that captures the beauty of a powerful moment in time.
The bright star in this picture has been more important than you might think.(Supplied: NASA/ESA, The Hubble Key Project Team and The High-Z Supernova Search Team)
It may just look like a bright star under a galaxy, but this simple image captures a powerful moment in time that is instantly recognisable by astronomers like Brad Tucker.
Dr Tucker studies supernovae — massive explosions that light up our universe — using the Australian National University's Mount Stromlo Observatory.
And that bright star below the galaxy is one of the most iconic images of a supernova ever taken.
"I love this photo of supernova 1994D," he says.
"You see a galaxy and just this 'bright star'. But then you realise that 'bright star' is 50 million light years away."
Not long after the dinosaurs vanished off the Earth, the star at the bottom of this image reached a critical mass (known as the Chandrasekhar limit) and exploded in a ball of powerful energy.
Fifty million years later the explosion on the outskirts of an old dusty spiral galaxy, NGC 4526, was captured by the Hubble Space Telescope.
"You would never see this with your eyes, it's so bright, yet so faint and far away, which I think is the elegance to it."
Supernovae are fleeting events lasting just weeks or, at best, a couple of months.
"So when we look back at [this galaxy] we can't see traces of that supernova. That star has completely gone."
"If we never saw that explosion, we would never have known that star system existed. And we would never have known that entire solar system just died."
The beauty of supernovae
Although the supernova looks like it is sitting by itself outside the galaxy, there are likely to be stars all around it that are too faint to see.
"Galaxies are 3D bodies. but we see them as 2D images so we kind of miss the depth in the field."
But that, said Dr Tucker, is the beauty of a supernova.
"When the entire thing explodes it goes ... from something that you don't even know exists to being so bright that it is brighter than almost the whole galaxy."
Supernova 1994D was snapped in early March 1994 in the constellation of Virgo.
Back then, the Hubble Space Telescope had just become functional and the study of supernovae was relatively young.
"These days a supernova with the name 'D' happens somewhere on January 1."
"It just goes to show how many of these things are out there, and yet back in the day, only 26 years ago it took a lot of effort to find this one."
Supernovae like this, known as type1a supernovae, play an important role in estimating the rate of expansion of the universe.
Astronomers calculate the distance between objects by measuring the brightness of the explosion.
Supernova 1994D was part of a small set of supernovae used to prove the universe was not only expanding, but the rate of expansion was accelerating, which led to the Nobel Prize-winning discovery of dark energy.
"Historically, it is part of research that proved 70 per cent of the universe was there that we didn't know of."
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