The Alternate View
LIGO’s GW190521 Mystery: Eccentric Orbit or Wormhole?
by John G. Cramer
Gravitational waves (GW) are traveling space-distortion ripples that arise when a massive object moves and its extended gravitational field is disturbed. They were first predicted by Albert Einstein in 1916, demonstrating a wave equation derived from his weak-approximation equations of general relativity. It took a long time for them to be directly detected, but well before their LIGO observation in 2015, their physical existence was inferred indirectly in 1974 by Taylor and Hulse from the observed loss of energy in the spin-down of a pair of merging neutron stars, producing radio waves that were detected with a radio telescope.
Like the electromagnetic waves of light, gravitational waves travel at the speed of light and obey the inverse-square law [intensity ~ 1/(distance)2]. They induce a quadrupole “kneading” distortion in space as they move through it, making local distances alternately longer and shorter. The traveling GW can be visualized as a long sausage, with its sides alternately pinched in side-to-side and then top-to-bottom, with the pinches along the length of the sausage repeating with each wavelength and the entire sausage moving forward at the speed of light.
Starting in the early twenty-first century, several laser interferometer systems with very long arms, capable of detecting these traveling space-time distortions, have come online. The first of these is LIGO (Laser Interferometer Gravitational-Wave Observatory), the U.S. National Science Foundation’s large-scale physics experiment designed to detect and analyze GW of cosmic origin. LIGO has been in operation since 2002 and, after a major upgrade, begin observing GW events starting in 2015. LIGO has two perpendicular 2-km-arm interferometer detectors. This configuration is duplicated at two widely separated sites in the U.S., one located in the desert environment of the Hanford Reservation near Richland in Washington State and the other located in a loblolly pine forest in Livingston, Louisiana. Recently this original two-site configuration of detectors grew and improved. LIGO has been joined by Virgo, the European GW detector located near Pisa, Italy, and the Kamioka Gravitational Wave Detector (KAGRA), located in Japan. The improved four-site configuration allows more precise extraction of the sky direction and wave polarization of the sources of the incoming detected GWs. At this writing, LIGO and its international helper detectors have observed a total of about 218 GW events.
On May 21, 2019, both LIGO and Virgo recorded a very unusual GW event, later given the name GW190521. It appeared in the sky of the Northern Hemisphere, coming from roughly the direction of Coma Berenices. The event showed a luminosity distance of 17 billion light years. This very large distance seems paradoxical, since the current estimate of the age of the universe, deduced from the cosmic microwave background, is only 13.8 billion years. However, because the universe is expanding, the “observable universe” has a radius of about 46 billion light years, the distance to the universe’s visible horizon where light waves are redshifted to zero and become
undetectable.
GW190521 was an unusual detection event because it did not show the usual spin-down signal preceding the GW merger flash, and it may have been accompanied by an intense flash of light. The first analysis of GW190521, assuming circular in-spiraling, indicated that the GW signal was best described as the result of the merger of two black holes with masses of about 85 and 66 solar masses. These would be the most massive pair of merging black holes ever observed by the GW detectors. The resulting post-merger black hole should have a mass of about 143 solar masses, with the remaining 8 solar masses radiated away as GW energy.
The large masses are particularly significant because astrophysics tells us that a star with a mass of more than about 65 solar masses cannot collapse to a black hole. Thus, both of the initial 66 and 85 solar mass objects and the final 143 solar mass object exceed this mass limit. Are these large black hole masses the net result of previous black hole mergers of smaller objects, or are they perhaps primordial black holes, created by direct production in the aftermath of the Big Bang? Both are possibilities, but the latter seems more likely.
As mentioned above, event GW190521 is unusual in two ways: (1) While most black-hole mergers emit no significant light or other forms of electromagnetic radiation, GW190521 may have been accompanied by the light flash detected by the Zwicky Transient Facility (ZTF), located at the Palomar Observatory in California. The ZTF recorded a light flash that occurred at the same time and was visible in the same region of the sky as the GW event. And (2) GW190521 was relatively short in duration and seemed to lack the long rising GW ring-down signal that usually precedes a black-hole merger event.
These unusual GW190521 characteristics have prompted some interesting follow-up analyses. Romero-Shaw et al. showed that the LIGO and Virgo data is better described by a highly eccentric binary orbit preceding the black hole merger. In a follow-up analysis, Gayathri et al. found that in such an eccentric-orbit scenario, the two merging black holes would have masses of about 102 solar masses each. These analyses make the high masses of the component black holes even more mysterious. However, they do not account for the unusual light flash that may have accompanied the GW event.
Recently, Lai et al have proposed a more radical alternative explanation of the unusual characteristics of GW19052. They suggest that the observed GW came from the merger of a ~100 solar mass and an ~80 solar mass pair of black holes located in another universe (or perhaps in a very distant part of our own universe), which for a time created a wormhole connection to the observed location of GW190521 in our universe. In their scenario, the observed GW signal is the echo of the resulting other-universe GW passing through the wormhole and into our universe. There is no preceding ring-down signal because the wormhole was only created in the final stages of the black hole merger.
Of course, this wormhole-echo scenario is very controversial, but it does produce nice fits to the LIGO and Virgo data. So the question is, how convincing are the data/calculation comparisons of the two alternative scenarios? The Lai-paper authors used Bayesian statistics to compare the fits to the LIGO and Virgo data with both scenarios, the eccentric-orbit model described above and their worm-hole-echo model. The result of this Bayesian comparison slightly favors the eccentric-orbit model, but the wormhole-echo model cannot be ruled out.
One deficiency of the Lai paper is that it does not consider the possibility of coincident electromagnetic radiation, as perhaps indicated by the ZTF light flash detection. We note that if any net electric charge, perhaps a stream of electrons, had passed through the hypothetical wormhole during its rather short period of existence, the subsequent wormhole pinch-off, severing the electric lines of force threading the wormhole throat, should have produced a large electromagnetic transient that could account for the intense ZTF light flash that was observed to be coincident with GW190521. Thus, the Lai wormhole-echo model could potentially explain more features of GW190521 than its more conventional rivals.
This is a science fiction magazine, so some of us have a particular interest in the possible existence of stable wormholes connecting to other universes or to remote parts of our own universe. In my two hard SF novels Einstein’s Bridge and Fermi’s Question, as well as novels by Peter Hamilton and others, stable transversable wormholes provide an important background to the stories. From this point of view, the hypothetical Lai wormhole, if it did exist in the early universe, is rather unsatisfying, because it probably had only a brief duration. It would have come into existence for only a very brief period during a black hole merger and likely pinched off again and disappeared well before much other than the gravitational waves generated in its creation could pass through it.
Nevertheless, it can be taken as possible evidence that wormholes do exist. That makes our universe a much more interesting place.
Hard SF Novels: John’s new 3rd hard SF novel, Fermi’s Question, and its prequel, his 2nd hard SF novel Einstein’s Bridge, are available as eBooks from Baen Books at: https://www.baen.com/einstein-s-bridge.html. His 1st SF novel, Twistor, is available online at: https://www.amazon.com/Twistor-John-Cramer/dp/048680450X.
Non-Fiction Books: John’s book describing his transactional interpretation of quantum mechanics, The Quantum Handshake—Entanglement, Nonlocality, and Transactions (Springer, January 2016) is available online at: https://www.amazon.com/dp/3319246402. John’s new book, Human Aging and Longevity: The Mitochondrial DNA Connection (Springer Copernicus), will be available in early 2026.
Alternate View Columns Online: Electronic reprints of 240 or more of “The Alternate View” columns written by John G. Cramer and previously published in Analog are currently available online at: http://www.npl.washington.edu/av.
References:
A. Einstein, “Näherungsweise Integration der Feldgleichungen der Gravitation,” Sitzungsberichte der Königlich Preußischen Akademie der Wissenschaften (Berlin), 1, 688—696 (1916); and “Über Gravitationswellen,” ibid. 154—167 (1918).
R. A. Hulse and J. H. Taylor, “Discovery of a pulsar in a binary system,” Astrophysical Journal Letters 195, L51-L53 (1975); https://doi.org/10.1086/181708.
R. Abbott, et al. “Properties and Astrophysical Implications of the 150 M⨀ Binary Black Hole Merger GW190521”. The Astrophysical Journal 900 (1): L13 (2020); arXiv:2009.01190.
I. Romero-Shaw, et al. “GW190521: Orbital Eccentricity and Signatures of Dynamical Formation in a Binary Black Hole Merger Signal,” The Astrophysical Journal 903 (1): 5 (23 October 2020); arXiv:2009.04771.
V. Gayathri, et al. “GW190521 as a Highly Eccentric Black Hole Merger”; arXiv:2009.05461 [astro-ph.HE] (2020).
Q. Lai, et al. “Is GW190521 a gravitational wave echo of wormhole remnant from another universe?”; arXiv:2509.07831v1 [gr-qc], (9 Sep 2025).