What’s the News: Astronomers have known for a while that white dwarfs can sometimes ignite in massive explosions known as Type Ia supernovae, but they haven’t been sure what pulls the trigger. One theory says that the explosion occurs when two white dwarfs merge into each other, while an opposing theory says that it happens when a single white dwarf pulls material from a Sun-like companion star. Using the Chandra X-ray telescope, astronomers have discovered an arc-shaped material emitting X-rays in the Tycho supernova that gives hints about the supernova’s origin. “This stripped stellar material was the missing piece of the puzzle for arguing that Tycho’s supernova was triggered in a binary with a normal stellar companion,” says Fangjun Lu. “We now seem to have found this piece.”
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What’s the News: While the Kepler spacecraft is busy finding solar system-loads of new planets, other astronomers are expanding our idea where planets could potentially be found. One astronomer wants to look for habitable planets around white dwarfs, arguing that any water-bearing exoplanets orbiting these tiny, dim stars would be much easier to find than those around main-sequence stars like our Sun. Another team dispenses with stars altogether and speculates that dark matter explosions inside a planet could hypothetically make it warm enough to be habitable, even without a star. “This is a fascinating, and highly original idea,” MIT exoplanet expert Sara Seager told Wired, referring to the dark matter hypothesis. “Original ideas are becoming more and more rare in exoplanet theory.”
How the Heck:
- Because white dwarfs are much smaller than our Sun, an Earth-sized planet that crossed in front of it would block more of its light, which should make these planets easier to spot. So astronomer Eric Agol suggests survey the 20,000 white dwarfs closest to Earth with relatively meager 1-meter ground telescopes.
- And because white dwarfs are so cool, a planet in a white dwarfs habitable zone would be very close, meaning its transit would happen very fast. Agol says we’d only need to watch a star for 32 hours to pick up on any transiting, habitable planets.
- One leading theory about dark matter is that it’s made of theoretical particles called WIMPS (weakly interacting massive particles). It’s thought that when WIMPs collide (if, of course, they exist), they would explode. Astronomers think that these WIMP explosions could possibly heat a planet enough to make it habitable.
- There are no immediate plans to test the dark matter hypothesis, which is quite theoretical, and any plan to find dark matter-fueled planets would need to look far from here: our part of the universe doesn’t have nearly enough dark matter to bring a planet to habitability.
What’s the Context:
Not So Fast:
- It’s not at all clear if white dwarfs have any planets, and if so, whether any of them could possibly support water or life as we know it. For one thing, planets in the habitable zone would be tidally locked with the star—permanent scalding daylight on one side; permanent frozen nighttime on the other.
- Taking 32 hours to find a planet orbiting a white dwarf may seem like a short time, but when you’re looking at tens of thousands of stars, it adds up. Agol told UW Today, “This could take a huge amount of time, even with [a network of telescopes].”
- And just like star-orbiting planets have their Goldilocks zones (not to hot or too cold), dark matter-containing planets would need the right amount of dark matter to be habitable. “It’s not something that’s likely to produce a lot of habitable planets,” Fermilab researcher Dan Hooper told Wired. “But in very special places and in very special models, it could do the trick.”
References: Eric Agol. “TRANSIT SURVEYS FOR EARTHS IN THE HABITABLE ZONES OF WHITE DWARFS.” doi: 10.1088/2041-8205/731/2/L31
Dan Hooper and Jason H. Steffen. “Dark Matter And The Habitability of Planets.” arXiv:1103.5086v1
Image: NASA/European Space Agency
Astronomers keep turning up new exoplanets, and as the count rises, they keep edging closer to finding worlds like our own pale blue dot. Astronomer Jay Farihi thinks Earth-like worlds might be even more common in the universe than previously expected, based on evidence from rocky planets few astronomers are studying: The ones that don’t exist anymore.
Farihi’s research subjects are white dwarfs. In our galaxy, about 90 percent of stars will end their lives in this incredibly dense state once the star sheds its outer material and only the core remains. This is the fate of our sun. White dwarfs usually have atmospheres composed of the light elements helium and hydrogen, as the heavy elements have settled to the core. But about 20 percent of white dwarfs are different, showing heavy elements—what astronomers call “metals”—in their atmospheres. For decades, astronomers attributed this metallic pollution to the interstellar medium, the thin gas that permeates the space between stars. The idea was that white dwarfs were old stars that had been on several orbits around the Milky Way and had picked up bits of the interstellar medium as they went around [Space.com]. But Farihi thinks those elements are evidence of something else.
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