Skip to Content
Uncategorized

White Dwarfs, Habitable Zones and Other Earths

Astronomers have ignored white dwarfs in their search for exoplanets. That may have been a mistake, according to a new study of white dwarf habitable zones

Although black holes and neutron stars get all the attention as the ultimate fate of stars, most will never make it that far. Some 97 per cent of the stars in our galaxy are not massive enough to form either.

Instead, astronomers believe they will end their days as white dwarfs, hot dense lumps of inert matter in which all nuclear reactions long ago burnt out.

These stars are about the size of the Earth and supported against gravity by the Pauli exclusion principle which prevents electrons occupying the same state at the same time.

The only radiation they emit is thermal heat as they cool, so it’s easy to imagine that these objects are of little interest to astrobiologists. And as it turns out, most searches for exoplanets have focused on nearby stars like our own.

Today, Eric Agol at the University of Washington in Seattle points out that planet hunters may be missing a trick. He says that white dwarfs could be good targets for exoplanet searches.

He points out that they are as common as Sun-like stars, that the most common ones have a surface temperature of about 5000 K and that this should produce a habitable zone at distances of about 0.01 AU for periods in excess of 3 billion years. That’s long enough for something interesting to have emerged on these bodies.

What’s more, any Earth-sized planet orbiting at this distance ought to be easy to spot as it passes in front of the tiny disc of a white dwarf.

There is a caveat, however. As stars age, they form red giants that engulf everything within a radius of about 1 AU. So any planet orbiting a white dwarf in the habitable zone would have to have migrated there after the white dwarf formed.

That’s a little discouraging but it’s not entirely impossible. Many theories of solar system formation assume that planet migration plays an important role.

Agol goes on to calculate many of the properties of these other Earth’s, which turn out to be surprisingly similar to our own. “Inhabitants of a planet in the [habitable zone] will see their star as a similar angular size and color as we see our Sun,” he says.

On the other hand, the short orbit and the possibility of tidal locking mean these planets will probably have a permanent day and and night side.

But what is most exciting about Agol’s work is that the deep transits in front of the parent star should make these planets easy to detect. “Earth-sized or even smaller bodies could in principle be detectable with ground-based telescopes,” says Algol. In fact, he reckons a network of twenty 1-metre sized telescopes systematically surveying the sky over 2 years could find half a dozen planets.

Which means there’s an outside chance that the first Earth-like planet could be found orbiting a white dwarf.

Ref: arxiv.org/abs/1103.2791: Transit Surveys For Earths In The Habitable Zones Of White Dwarfs

You can now follow The Physics arXiv Blog on Twitter

Keep Reading

Most Popular

conceptual illustration of a heart with an arrow going in on one side and a cursor coming out on the other
conceptual illustration of a heart with an arrow going in on one side and a cursor coming out on the other

Forget dating apps: Here’s how the net’s newest matchmakers help you find love

Fed up with apps, people looking for romance are finding inspiration on Twitter, TikTok—and even email newsletters.

computation concept
computation concept

How AI is reinventing what computers are

Three key ways artificial intelligence is changing what it means to compute.

still from Embodied Intelligence video
still from Embodied Intelligence video

These weird virtual creatures evolve their bodies to solve problems

They show how intelligence and body plans are closely linked—and could unlock AI for robots.

We reviewed three at-home covid tests. The results were mixed.

Over-the-counter coronavirus tests are finally available in the US. Some are more accurate and easier to use than others.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.