Astronomers spot never-before-seen gravitational wave source from binary white dwarf stars

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By Chelsea Gohd
last updated

An artist's visualizatoin of the first confirmed double helium-core white dwarf gravitational source. (Image credit: M. Weiss)

Astronomers have detected two stellar corpses whirling around each other, and they might be producing gravitational waves. 

White dwarf stars are what become of stars like our sun after they run out of fuel and turn into leftover hot cores. For many years, researchers have predicted that there should be binary, or two-object, systems made up of white dwarf stars. According to general relativity, two such masses orbiting each other should emit energy in the form of gravitational waves, which are ripples or disturbances in the fabric of spacetime. 

Now, this is not the discovery of gravitational waves, rather it is the discovery of this binary which may be a source for gravitational waves. But, not only will this study advance our understanding of these systems and gravitational wave sources, it will also be important in validating the efficiency of an instrument that will launch in 2034. 

Video: Double star system is a 'cosmic Jekyll and Hyde'
Related: Is life possible around binary stars? (Podcast)

The instrument, LISA (the Laser Interferometer Space Antenna) gravitational wave observatory, will use the J2322+0509 system to essentially train with. Because they already know they exist, it's a good test to make sure the instrument can correctly spot it.

"Verification binaries are important because we know that LISA will see them within a few weeks of turning on the telescopes," Mukuemin Kilic, a co-author on this study from the University of Oklahoma, said in the statement. "There's only a handful of LISA sources that we know of today. The discovery of the first prototype of a new class of verification binary puts us well ahead of where anyone could have anticipated."

In a new study identifying and exploring this binary, researchers at the Center for Astrophysics (CfA) at Harvard have detected, for the first time, a binary white dwarf system made up of two white dwarf stars (with helium cores) that are clearly separate stars. This system, known as J2322+0509, has a short orbital period of 1,201 seconds (just over 20 minutes) and is the first gravitational wave source of its kind ever identified. 

"Theories predict that there are many double helium-core white dwarf binaries out there," Warren Brown, CfA astronomer and lead author on the study, said in a statement. "This detection provides an anchor for those models, and for doing future experiments so that we can find more of these stars and determine their true numbers."

This system, whose orbital period is the third shortest period of all detached binaries ever found, was fairly tough to spot. "This binary had no light curve," Brown said in the statement. "We couldn't detect a photometric signal because there isn't one." So instead of using a photometric study, which looks at light itself, the team used spectroscopic studies, which observe how matter interacts with electromagnetic radiation like visible light, to identify the star's orbital motion.

But, while the system was tricky to spot, it turns out that this type of binary is an extremely strong source of gravitational waves, the team found using theoretical calculations, according to the statement and the study. The researchers determined that because of the system's alignment with respect to Earth, instruments should pick up a signal 2.5 times stronger than from the same system twisted a different direction. 

This binary won't be a binary forever, though, as a consequence of the very gravitational waves the scientists hope to someday detect. "The orbit of this pair of objects is decaying," Brown said. "The gravitational waves that are being emitted are causing the pair to lose energy; in six or seven million years they will merge into a single, more massive white dwarf."

This work is described in a paper posted to the preprint server arXiv.org on April 3 that has been accepted by the journal Astrophysical Journal Letters. 

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Chelsea Gohd
Chelsea Gohd
Senior Writer

Chelsea “Foxanne” Gohd joined Space.com in 2018 and is now a Senior Writer, writing about everything from climate change to planetary science and human spaceflight in both articles and on-camera in videos. With a degree in Public Health and biological sciences, Chelsea has written and worked for institutions including the American Museum of Natural History, Scientific American, Discover Magazine Blog, Astronomy Magazine and Live Science. When not writing, editing or filming something space-y, Chelsea "Foxanne" Gohd is writing music and performing as Foxanne, even launching a song to space in 2021 with Inspiration4. You can follow her on Twitter @chelsea_gohd and @foxannemusic.

13 Comments Comment from the forums
  • JPL-ACE
    I pay less attention to your otherwise decent articles because of your Click Bait titles. Please tone it down. The info is interesting in its own right. It is important to have this binary as a calibrator for LISA but your title implies the waves are already discovered gravitationally. Bad dog!
    Reply
  • Moni999
    I kind of agree with JPL-ACE.
    Reply
  • Torbjorn Larsson
    This is a matter of personal opinion, in a context of that titles aim to be click baits. In my eyes the title is descriptive of the article, so I'm happy with that. It would be even better if the title was neutral, of course, but it's a readers market. So like JPL-ACE, I vote with my feet - the articles appears in my feed, I can browse titles and source, and try to assess real click value.

    I look forward to an AI pre-reader app, that tries to weed the chaff to my liking, but at the same time balance the unavoidable bias market pressures puts on web browsers and their search mechanisms based on my previous reading. I would want to switch between a narrow "nerd" and a neutral "news" mode. Even better, the app would do it for me at some preset ratio of my choosing (unless I override).
    Reply
  • dfjchem721
    "Astronomers spot never-before-seen gravitational wave source from binary white dwarf stars"

    Actually the title is completely accurate, and very interesting. Few (if any) with significant knowledge of gravitational waves (GWs) would find this article to be click bait. Most would find it to be very interesting. If it is bait, it is fishing for some major data!

    The title clearly states that the binary is a "source", but does not indicate that the system produces currently detectable GWs, which is also clearly noted in the article. All astronomical systems with mass produce GWs. According to the link below, our solar system puts out 5000 watts in GWs, trace levels to be sure. Nothing in the title suggests they have measured waves from these dwarfs, merely that they are a "source" (which they certainly are!).

    I was in fact surprised to see that such small orbiting objects would produce detectable GWs. Then realized that they could not be observed using LIGO. My reading in the past is that GWs have only been seen in mergers of large black holes and neutron stars, where massive objects rapidly accelerate at the moment of merging to create powerful GWs. Our observations of GWs from these events is limited to the low sensitivity of the LIGO instruments, and distance and masses to the merging objects.

    In order for the white dwarf star binary to be emitting significant, detectable levels of GWs, the orbit must be decaying (as noted) and therefore the dwarf stars are accelerating more and more rapidly, thereby generating ever stronger GWs. The point of the article is the binary may be a source for GWs that more advanced instruments could detect and measure, without requiring a merger. Such a quasi-stable GW source is likely to be of significant observational value. But you need to find such a binary first, and now they have. Nothing in the title suggests they detected GWs, only that the dwarfs' would be a source for future study (with more sensitive instruments like LISA).

    There is another binary, a neutron binary, which actually was the first to demonstrate, although less directly than LIGO, GWs from two orbiting neutron stars. At least the Nobel Committee was impressed by this discovery (whatever that is worth):

    https://en.wikipedia.org/wiki/Hulse%E2%80%93Taylor_binary
    The present observation makes the discovery (or title) of two close and rapidly orbiting dwarf stars significantly more than click bait.
    Reply
  • mike215
    Nope it is definitely clickbait. The article title says they spot the gravitational waves source from the binary. Quite different from spotting a potential gravitational wave source that is a binary. And I'm familiar with gravitational waves as I do have a MS in physics.
    Reply
  • dfjchem721
    The title refers to a source for GWs. The binary dwarf stars do not have "potential" to create GWs. They WILL create GWs. (To clarify - there is no option B.)

    One needs a sensitive enough instrument to detect them. They are emitting these GWs as I write this!

    How could this be more obvious?
    Reply
  • dfjchem721
    An interesting note on the energy from gravitational wave sources:

    GW150914, a merger of two black holes of about 30 SMs each, spit out intense GWs during merger, losing ca. 3 SMs with a peak power output of 3.6 × 10^49 watts. This is claimed to be "more than the combined power of all light radiated by all the stars in the observable universe put together."

    https://en.wikipedia.org/wiki/Binary_black_hole
    That compares with 5 x 10^3 watts for GWs from our solar system. A tad more to be sure!
    Reply
  • mike215
    dfjchem721 said:
    Perhaps you need to go back to school. The title refers to a source for GWs. The binary dwarf stars do not have "potential" to create GWs. They WILL create GWs. (To clarify - there is no option B.)

    One needs a sensitive enough instrument to detect them. They are emitting these GWs as I write this!

    How could this be more obvious?
    "Spotting" a gravitational source did not occur if the detector isn't capable/didn't detect it, which was the point of the article. You assume LIGO and such can detect GW that feeble.
    Reply
  • dfjchem721
    I specifically said that LIGO could not detect them*, but that a more sensitive instrument would be needed. ::: Directly from your above repeat of my post - "One needs a sensitive enough instrument to detect them. "

    * And from my post of Monday @1:31 pm

    "I was in fact surprised to see that such small orbiting objects would produce detectable GWs. Then realized that they could not be observed using LIGO. "

    So "Spotting" a gravitational source" is not the same as getting the GW signal. The source is certainly generating GWs - the title merely noted a source. Which of course it is. And there is still no option B, and never will be.
    Reply
  • Wolfshadw
    Let's watch the attitude, people.

    Wolfshadw
    Moderator
    Reply