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Can we see dead stars with the naked eye?

Can you name any dead stars whose light is still visible to the naked eye?

When a star 'dies' (by that I mean when there are no more nuclear fusion reactions going on in it), it can take three different forms. Depending on the initial mass of the star, it will become either a white dwarf, a neutron star or a black hole.

You can immediately rule out seeing black holes because they don't emit any light, and neutron stars because they are too small. This leaves us with white dwarfs, which are the larger of the three possible end products for stars. Unfortunately, you will not be able to see even the brightest white dwarf. Astronomers describe the brightness of stars by their magnitude. The magnitude scale goes backwards such taht a star with magnitude 4 is fainter than a star with magnitude 1. With the naked eye and a clear sky, you can see stars about up to magnitude 6, and it turns out that the brighest white dwarf has a magnitude of 8.3. Moreover, that brightest white dwarf is in a binary system: it is the companion of the brightest star in the night sky: Sirius (that star is called Sirius A and its white dwarf companion is Sirius B). This makes it even more difficult to see, since the light from Sirius A overwhelmes that from Sirius B. But still, you can look at Sirius and imagine you are looking at two stars, one of which is a white dwarf!

The other idea would be to look at other remnants of stars: planetary nebulae. When a star dies and becomes a white dwarf, it ejects some gas into space that appears to glow because it is illuminated by stars. If you can see a planetary nebula, it means that there is a white dwarf in the centre of it. But once again we fall out of luck, since the brightest planetary nebula, the dumbbell nebula, has a magnitude of 7.4, which means you cannot see it with the naked eye.

November 2002, Amelie Saintonge (more by Amelie Saintonge) (Like this Answer)

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