Are the stars we see in the sky actually 'dead'?
Are the stars we see in the sky actually 'dead'?
Hello everyone,
Looking up at the stars at night you might remember a common claim that most of the stars see have already died. As the stars are so far away and it takes so long for their light to reach us, we are catching a glimpse of their former glory. To check if this claim is true, so we asked 8 experts in astronomy and astrophysics, ‘Are the stars we see in the sky actually dead?’, here is what they said…
EXPERT CONSENSUS
Are the stars we see in the sky actually 'dead'?
7 out of 8 experts say ‘No’
How far away are the stars we can see in the sky?
Light travels at about 300,000 kilometres per second (186,000 miles) in a vacuum. Stars are so far away from us that we don’t measure the distance is kilometres or miles, but in light years, which is the distance that light travels in one year. A light year is about 9 trillion kilometres or 6 trillion miles.
Most stars are so far away it takes years for their light to reach the earth, so we are looking at the light emitted from the stars many years ago. Our closest star, the sun, is about 8.3 light-minutes away; so, when we look at the sun, we are seeing what it looked like a few minutes ago. Dr Michael Boyle, an astrophysics and astronomy expert from Cornell University in the USA, says the stars we see in the sky “are usually no more than about 10,000 light years away, so the light we see left them about 10,000 years ago.”
How long do stars live?
Stars have a life cycle. They begin as a cloud of dust and gas which gets pulled together by gravity and creates a star. The star then passes through different phases with changes in size and colour before it ‘dies’, turning into a black dwarf, black hole or neutron star.
Dr Nathan Bourne, an astronomy and astrophysics expert from Edinburgh University in Scotland, says that “More massive stars burn more vigorously and burn out faster, but even the most massive live for a few million to 10 million years, although they are very rare. The majority of stars are dwarfs like the Sun, with lifetimes of anything up to 10 or 20 billion years.”
So, are the stars we are looking at alive?
If we know roughly how long stars live for and how far away they are, we can estimate how many of the stars we can see are already dead. All experts agreed that most stars we can see by eye (without a telescope) are still alive.
Professor Chris Tinney, an astronomy and physics expert from UNSW in Australia, says “While it is true that the light we see from distant stars is telling us about their state in the past (i.e. light from a star 3.3 light years away is telling us the star was emitting light 3.3 years ago), there are robust models for how stars work that tell us the majority of stars have lifetimes that massively exceed the time it has taken for light from those stars to get to us”
Dr Bourne, says “the chances of any one [star] dying within a given 1000 year window (say) are very small, so only a small number will do so.” He goes on to say that “Even if you use a large telescope to look deeply enough to see the far edges of the Galaxy, you are only looking at stars around 6000 light years away. The Andromeda galaxy is the most distant object visible to the naked eye, and the light from there has travelled through space for around 200,000 years to reach us. While we cannot see individual stars in that galaxy without a powerful telescope, a very small fraction of the stars will have died in the intervening time.”
More powerful telescopes will see a higher percentage of dead stars. Dr Bourne says “the most distant galaxies that astronomers study are seen as they were up to 13 billion years in the past, so many of their stars will have died by now”
The takeaway:
Only a small fraction of the stars we can see with the naked eye are ‘dead’.
May the facts be with you!
Eva
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