Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
In May of 2019, a short-duration binary black hole (BBH) merger contained no evidence of the inspiral signal typical of these kinds of a gravitational wave events.<\/p>\n
A new preprint argues that astrophysicists can\u2019t completely rule out the possibility that this signal could actually be a gravitational wave echo that traveled through the throat of a wormhole.<\/p>\n
Although the study\u2019s models claim that such an outcome is statistically possible, Bayesian factoring suggests that a BBH merger is still the most likely explanation.<\/p>\n
When the Laser Interferometer Gravitational-wave Observatory (LIGO<\/a>) detected the very first gravitational wave in 2015, it began a new era of astronomy. It gave scientists a new tool for observing and recording some of the most energetic phenomena in the known-universe\u2014things like supernovae, neutron star collisions, and black hole mergers. Since that first gravitational wave detection (which is called GW150914 and was produced by a black hole merger), LIGO has detected hundreds more, and some of these gravitational waves have inspired new and strange questions.<\/p>\n Case in point\u2014the gravitational wave detection known as GW190521.<\/p>\n As its name suggests, GW190521 rippled across the Earth on May 21, 2019 (gravitational wave detections are named for their dates of detection, in year-month-day order). The merger of two black holes itself isn\u2019t what causes the gravitational waves<\/a> we can detect\u2014rather, it\u2019s the interacting gravitational fields from two massive objects spiraling closer and closer together that create ripples in space-time. As shown with the detection of GW150914 in 2015<\/a>, this typically results in an audible \u201cchirp\u201d that looks like a rising waveform.<\/p>\n However, GW190521 lacks this rising signal, otherwise known as the \u201cinspiral\u201d part of the signal. What\u2019s strange is that the resulting black hole lies in the intermediate-mass rang (around 142 times the mass of our Sun<\/a>), so LIGO should have detected the tell-tale inspiral.<\/p>\n This has led some astronomers to ponder alternative ways that these two black holes<\/a> could have merged. One idea is that these black holes were caught in a mutual gravity well, essentially allowing them to skip the inspiral signal typically associated with black hole mergers. Others have pondered whether the black holes merged in an Active Galactic Nucleus<\/a> (AGN), which could help explain this massive binary system with current astrophysical models.<\/p>\n But a new paper uploaded by a team of Chinese scientists to the preprint server arXiv<\/a> has another, more extreme-yet-fascinating proposal: Maybe it\u2019s evidence of a wormhole<\/a>?<\/p>\n \u201cThe ringdown signal after binary black holes (BBHs) merged in another universe can pass through the throat of a wormhole and be detected in our universe<\/a> as a short-duration echo pulse,\u201d the authors wrote. \u201cWe hypothesize that GW190521 might represent a single, isolated gravitational wave (GW) echo pulse from the wormhole, which is the post-merger remnant of BBHs in another universe and connected to our universe through a throat.\u201d<\/p>\n This is a \u201cwoah if true\u201d assertion, and likely takes the idea of \u201cleaving no stone unturned\u201d to the scientific extreme, especially because wormholes themselves are completely theoretical. An Einstein-Rosen bridge<\/a>\u2014a mathematical solution for a specific wormhole\u2014requires exotic matter (i.e. negative energy density) in order to be stable. However, when the research team compared their model\u2019s network signal-to-noise ratio with that of a BBH merger model, the results were remarkably similar. Using Bayesian statistics to determine the most likely outcome, the BBH model is still preferred, but it\u2019s not significant enough to rule out a wormhole solution.<\/p>\n \u201cIt might be expected that future enhancements to the echo-for-wormhole waveform templates, incorporating more detailed physical characteristics, hold the potential to significantly improve the corresponding Bayesian factor,\u201d the authors wrote.<\/p>\n