Scientists have discovered a pair of white dwarfs that might one day produce a major gravitational wave discovery, according to a new paper.
Certain chaotic events, like black holes slamming together, produce waves of warping spacetime that physicists have spotted here on Earth. But other events, like dense objects quickly orbiting each other, can produce gravitational waves undetectable by current experiments, so scientists are building a space-based gravitational wave detector called the Laser Interferometer Space Antenna (LISA). Two newly discovered binary white dwarfs appear to be a prime source for the gravitational waves that LISA could detect.
“An object like this is really a gold mine for advancing our understanding of how the universe works,” Kevin Burdge, the study’s first author and a graduate student at CalTech, told Gizmodo.
The researchers first spotted evidence of the binary using the Zwicky Transient Facility at Palomar Observatory in California. That same night, another telescope on Kitt Peak in Arizona spotted the same source, and noticed that every 6.91 minutes its light dipped. Later, the researchers confirmed this light-dipping behavior with the another telescope at Palomar, and finally, observations using the W.M. Keck Telescope on Mauna Kea confirmed the velocity at which the stars were orbiting each other.
The researchers concluded that they’d spotted eclipsing white dwarfs. White dwarfs are small, dense objects that mark the end of life for most stars, probably including our own Sun one day, and these two were orbiting one another in such a way that one would block out the light from the other, as viewed from Earth. The mere fact that these white dwarfs eclipse one another is an important discovery, since it will allow scientists to make measurements of both stars that would be difficult to make otherwise, like their radii and brightness.
And they’re a weird pair of stars. It seems as if one is far hotter than a typical white dwarf, perhaps because it’s sucking up matter from the other. But observations haven’t found any evidence of this sort of behavior yet. The researchers will follow up with Hubble observations to see if they can find out what’s causing the temperature difference between the stars.
More exciting than binary white dwarfs, though, is the potential science that they can make possible. This binary is only around 7,500 light-years away, and its components orbit relatively close together, within a space smaller than the diameter of planet Saturn. Imagine how wild that is: Two bodies, one around half the mass of the Sun and the other a quarter the mass of the Sun, orbiting one another at that distance in less than seven minutes. That level of extremeness makes it one of the best targets for the upcoming LISA.
“[This source] is a strong source of gravitational radiation close to the peak of LISA’s sensitivity,” the authors write in the study published in Nature, “and we expect it to be detected within the first week of LISA observations, once LISA launches in approximately 2034.”
The mere existence of this system is exciting, said Warren Brown, astronomer at the Harvard-Smithsonian Center for Astrophysics who reviewed the paper, since it implies that more such objects are in the sky waiting to be discovered. It also gives researchers a jumpstart on what gravitational wave-emitting objects should look like in the sky before they’ve even seen the waves. “You can combine measurements of light now with measurements of gravity in the future,” Brown said. “It’s an interesting laboratory.”
Comparing gravitational waves, exploring potential causes of supernovae, and mapping the galaxy are just a few of the things that a source like this can assist with, Burdge told Gizmodo. Now, scientists just need to find more of them.
Clarification: A previous version of this article said that the white dwarf binary system could fit within our solar system; more accurately, the binary could fit within the diameter of the planet Saturn, according to the paper.
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