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Negative-Mass Binaries Generate Never-Seen-Before Gravitational Radiation

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In recent months, two papers (accessible here and here) suggested the existence of an abundant population of negative mass objects in the Universe. Albert Einstein’s theory of gravity, General Relativity, allows negative masses, as discussed in a seminal 1957 paper published here by the physicist Herman Bondi. In 2015, Robert Forward showed in a paper available here how negative masses can be used for propulsion without fuel. But as I explained in a recent essay here, we have no idea whether negative masses can be constructed in reality. In fact, their existence would create fundamental problems in our current understanding of the physical world. For example, negative masses can be used as building blocks in engineering a time machine which would violation causality, as I explained in an earlier essay here.

In principle, there are three types of mass:

1. Inertial mass, namely the mass given by the ratio between the force acting on an object and its resulting acceleration.

2. Active gravitational mass, namely the mass that generates the gravitational field around the object and affects the motion of other objects.

3. Passive gravitational mass, namely the mass that couples the object to the external gravitational field generated by other objects.

Momentum conservation requires that the active and passive gravitational masses would be equal. Otherwise, the momentum gained by one object will not necessarily be balanced by the momentum lost by another object when the two interact gravitationally with each other. Momentum conservation is a consequence of spatial translational symmetry, namely the invariance of the laws of physics to shifting a system from one position to another. Therefore, it is a sacred principle that cannot be violated.

The equality of the inertial mass and the passive gravitational mass is a fundamental assumption, called the Equivalence Principle, in Einstein’s theory of General Relativity. It rests on a pioneering experiment by Galileo Galilei at around 1590 and numerous follow-up experiments, which demonstrated that all objects accelerate the same way under the action of gravity irrespective of their mass or composition. In discussing negative mass objects, it is often assumed that conservation of momentum and the Equivalence Principle are both valid, and so all three forms of mass are the same.

However, the Equivalence-Principle rests on observational data for positive masses and could potentially be violated for negative masses. A new paper (available here) that I just co-authored with the brilliant PhD student, Oem Trivedi, shows that a system made of two objects which possess different values of the ratio between their gravitational and inertial masses would emit dipole gravitational radiation instead of the usual quadrupole gravitational radiation. The situation is analogous to a system made of positive and negative electric charges with positive inertial masses. So far, no sign of dipole gravitational radiation has been detected by the LIGO- Virgo-KAGRA (LVK) gravitational wave observatories. Current limits on dipole gravitational radiation are tight, as discussed here.

But even if the Universe contains only negative masses which satisfy the Equivalence Principle, binary systems containing such masses are expected to generate never-seen-before gravitational-wave signals:

1. Systems with a negative total mass are repulsive and short lived, preventing the formation of stable binaries.

2. Systems with a positive total mass, where the negative mass is smaller in magnitude than the positive mass, can form circular orbits. However, their evolution under gravitational radiation leads to expansion rather than inspiral, producing anti-chirp signals with decreasing frequency. Such a waveform is opposite to the chirp observed for all gravitational wave sources so far by LVK. The absence of anti-chirp signals in current gravitational wave catalogs provides a direct observational constraint on negative mass binaries. For an ordinary positive-positive binary, the orbital energy is negative and becomes more negative as the binary separation decreases, so gravitational-wave energy loss drives the system toward inspiral and increasing frequency. For a positive-negative binary with a positive total mass, the orbital energy starts being positive and decreases toward zero as the binary separation grows, so the same loss of gravitational-wave energy causes the system to expand rather than contract.

3. Systems with a zero total mass, where the negative mass cancels the positive mass precisely, correspond to runaway solutions where the pair accelerates up to the speed of light in some direction rather than engage in periodic motion.

So far, the new observational frontier of gravitational wave astrophysics did not lead to the discovery of new unexpected sources in our Universe over the past decade. This is somewhat disappointing and out of line with the history of astronomy, where observatories in a new band of the electromagnetic spectrum always revealed new unexpected sources. This was the case with radio telescopes discovering the cosmic microwave background, complex interstellar molecules or fast radio bursts; X-ray telescopes discovering accreting black holes, the cosmic X-ray background or X-ray clusters, and gamma-ray telescopes discovering gamma-ray bursts, gamma-ray pulsars or the cosmic gamma-ray background.

Our new paper shows that binary systems with negative mass members would generate gravitational-wave signals with never-seen-before properties. They provide novel targets for gravitational wave observatories which could either find them or rule them out.

ABOUT THE AUTHOR

1*LE3Xlzc3hNG5VDAGlDP8KQ.jpeg
(Image Credit: Chris Michel, National Academy of Sciences, 2023)

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.

Professional website:

https://lweb.cfa.harvard.edu/~loeb/

Social media:

https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb

https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb

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    • Avi Loeb Medium
      Linking the Non-Gravitational Acceleration of 3I/ATLAS to Its Symmetric System of Three Jets
      By Avi Loeb Medium
      The symmetric system of three jets emanating from the nucleus of the interstellar object 3I/ATLAS (separately from the primary anti-tail jet) after the circularly symmetric glow was removed by the Larson-Sekanina rotational gradient filter, based on a Hubble Space Telescope image taken on November 30, 2025. (Image credit: T. Scarmato and A. Loeb 2026)A new paper (accessible here) that I co-authored today with Toni Scarmato analyzed images of the interstellar object 3I/ATLAS, taken by the Hubble Space Telescope over the past five months. After removing the circularly-symmetric glow around the nucleus of 3I/ATLAS using the Larson-Sekanina rotational gradient filter, we identified three jets emanating from the nucleus that are equally separated from each other in sky projection by about 120 degrees in addition to a primary anti-tail jet pointed at the Sun.
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    • Avi Loeb Medium
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      The cores of globular clusters are known to contain an abundant population of neutron stars which appear as pulsars or X-ray sources with a mass of up to twice the mass of the Sun (as discussed recently here). These neutron stars, remnants from core collapse of massive stars, have a mass density of an atomic nucleus and a characteristic size of a city, about 12 kilometers (as discussed here).
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      ABOUT THE AUTHOR
      (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
      Professional website:
      https://lweb.cfa.harvard.edu/~loeb/
      Social media:
      https://avi-loeb.medium.com/
      https://www.youtube.com/@ProfessorAviLoeb
      https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
      https://x.com/ProfAviLoeb
      View the full article
    • Avi Loeb Medium
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      Far from the Sun, their energy is purely in the form of kinetic energy (per unit mass):
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      E = -GM/r + (1/2) v²
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      However, the situation changes under the action of a non-gravitational force, such as the rocket effect from outgassing. Let us restrict our attention to the simple case of a non-gravitational acceleration, A[r], that scales similarly to gravity as 1/r² (as was the case for 1I/`Oumuamua or 3I/ATLAS) and always points opposite to the object’s velocity, namely away from the Sun before perihelion. In this case, the energy E of the interstellar object will be reduced by A*r as the object arrives from interstellar space to a distance r from the Sun. The reduction in energy results from the fact that this non-gravitational acceleration allows down the object and reduces its positive kinetic energy. The effect is equivalent to pumping the breaks on a vehicle.
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      The condition for an interstellar object to be trapped by the Sun owing to its non-gravitational acceleration is A*r > (1/2) U², or equivalently:
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      This can be compared to the gravitational acceleration at a distance r from the Sun, g=(GM/r²) = (v_e^/2r).
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      ***
      Consider the example of the interstellar object 3I/ATLAS which entered the Solar System with an interstellar speed of U = 58 kilometers per second. The escape speed at its perihelion distance of 1.36 times the Earth-Sun separation is v_e = 36 kilometers per second. In order for 3I/ATLAS to slow down enough and stay in the Solar System, the object had to break with a non-gravitational acceleration that is larger than the gravitational acceleration by a factor of
      A/g > (58/36)² = 2.6
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      A/g ~ 0.0001
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      ***
      Today, the NSF-DOE Rubin Observatory released its data preview here. The full Rubin database over the coming decade is expected to reveal dozens of new interstellar objects. If any of them appears to slow down enough to become gravitational bound to the Solar System, this breaking should be regarded as a strong enough technological signature to elevate its rank close to 10 on the Loeb Classification Scale of interstellar objects (as discussed here, here and here).
      ABOUT THE AUTHOR
      (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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      https://lweb.cfa.harvard.edu/~loeb/
      Social media:
      https://avi-loeb.medium.com/
      https://www.youtube.com/@ProfessorAviLoeb
      https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
      https://x.com/ProfAviLoeb
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    • Avi Loeb Medium
      The Non-Gravitational Acceleration of 3I/ATLAS is Not Directed Away from the Sun
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      Orbit of 3I/ATLAS relative to the Sun in the ecliptic plane of the Earth around the Sun (with 1au being the Earth-Sun separation). Closest approach (perihelion) is marked by a yellow star, and the endpoints of the observational arc used for the orbit determination are indicated by open circles. Gray shading denotes the region where 3I/ATLAS goes under the orbital plane of Earth around the Sun, as the retrograde orbit of 3I/ATLAS is inclined by 5 degrees relative to the ecliptic. The Sun and the orbits of the major planets out to Jupiter are shown for reference. (Image credit: F. Spada, M. Królikowska and L. Dones, in a paper posted here on March 3, 2026)Today, a new paper reported the most comprehensive analysis of the non-gravitational acceleration of the interstellar object 3I/ATLAS. Its results differ from the official NASA report, posted on the Jet Propulsion Laboratory (JPL) Small Body Database here.
      Whereas NASA reports a radial acceleration component away from the Sun that is 5 times larger than the tangential component along the direction of motion of 3I/ATLAS, the new paper derives similar amplitudes for the radial and tangential components. The new analysis suggests that 3I/ATLAS is pushed sideways and not simply away from the Sun — as implied by the official analysis of Davide Farnocchia from NASA/JPL. Yes, official statements from NASA can be wrong. Science is a learning experience.
      Does a large non-radial acceleration make sense? Yes, according to high-resolution images of 3I/ATLAS. Observations from August 2026 when 3I/ATLAS was approaching the Sun, reported here the existence of collimated, high-latitude jets that display a periodic wobble consistent with nucleus rotation. This morphology indicated localized sources of mass loss rather than uniform sublimation of the nucleus, which could trigger significant non-radial acceleration. In two papers that I co-authored with Toni Scarmato here and here, we removed the circular glow around the nucleus in the highest-resolution post-perihelion images of 3I/ATLAS from the Hubble Space Telescope, and discovered three symmetrically-separated mini-jets in addition to a prominent sunward jet (anti-tail), modulated by a 7.1 hours rotational period and consistent with a spin-axis orientation within 20 degrees of the sunward direction. Such a configuration naturally favors strongly directional gas and dust emission, capable of generating a transverse acceleration component which is comparable in magnitude to the radial one. It would be interesting to use the geometry of this jet system and demonstrate that the non-gravitational force on the nucleus yields a tangential acceleration comparable in magnitude to the radial one, based on the mass outflow carried by the different jets.
      The conclusions of the new paper are based on examining a variety of orbital solutions that implement symmetric, time-offset, and asymmetric radial dependence of the outgassing relative to perihelion. The radial and normal components of the non-gravitational acceleration (labeled, A1 and A3) are broadly consistent across all solutions, whereas the transverse component (A2) is more sensitive to data selection, parameter correlations, and orbital phase coverage. The magnitude of the non-gravitational acceleration can be used to constrain the nucleus diameter of 3I/ATLAS, which most recently was inferred here to be 2.6 kilometers.
      The total magnitude of the non-gravitation acceleration is small, about a micrometer (a percent of the width of a human hair) per second squared. It corresponds to a spatial offset by half the radius of the Moon over a period of a month. This offset is smaller than the Earth-Sun separation by a factor of 200,000 and is therefore of negligible significance in shifting the path of 3I/ATLAS relative to the Sun or the planets.
      The origin of the symmetric system of 3 mini-jets, separated equally by 120 degrees from each other, remains enigmatic. Does it constitute a technological signature of thrusters? We do not know.
      ***
      Before my morning jog at sunrise, I received the following uplifting message from the poet Alan Wagstaff in New Zealand.
      “Dear Dr Loeb,
      You said in a recent essay:
      ‘This could be done by attending a science-fiction movie, subscribing to belief cults on social-media, using metaverse goggles or taking recreational drugs. These virtual realities bend constraints at will and give rise to a pleasing experience that makes us happy. ‘
      May I add, science imaginings sometimes provide the impulse which launches clear thinkers into science proper? So long as fact and fiction are not conflated, this is positive. As Robert H. Goddard once said in a letter to H. G. Wells:
      “In 1898 I read your ‘War of the Worlds’. I was sixteen years old … It made a deep impression … The spell did not break … and I took up physics.”
      (Goddard went on to become a foundational figure in rocketry and launch physics, eventually pioneering liquid-fueled rockets that laid the groundwork for the Space Age.)
      In the light of this, I revisited my poem ’Three Magi’ and honed it. Perhaps it will light a spark somewhere that will provoke real science in some young student’s mind.
      Kind regards
      Alan”
      ABOUT THE AUTHOR
      (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
      Professional website:
      https://lweb.cfa.harvard.edu/~loeb/
      Social media:
      https://avi-loeb.medium.com/
      https://www.youtube.com/@ProfessorAviLoeb
      https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
      https://x.com/ProfAviLoeb
      View the full article
    • Avi Loeb Medium
      3I/ATLAS Maintained a Sunward Jet After Its Gravitational Deflection by 16 Degrees at Perihelion
      By Avi Loeb Medium
      Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)The near alignment of the rotation axis of the interstellar object 3I/ATLAS with the sunward direction at large distances (as discussed here and here) could have been spoiled after perihelion.
      The rotation axis can remain fixed if no torque acts on 3I/ATLAS. However, the direction of motion of 3I/ATLAS was shifted by the following angle (in radians) at perihelion:
      2GM/(b*v²)= 0.286=16.4 degrees,
      where G is Newton’s constant, M is the mass of the Sun, b=202 million kilometers is the perihelion distance and v=68 kilometers per second is the perihelion speed.
      Remarkably, this deflection angle is twice the opening angle of the anti-tail jet, which was observed to span about 8 degrees out to a distance of order a million kilometers in the latest images of 3I/ATLAS from December 15, 2025 (as discussed here). If one edge of the jet’s cone overlapped with the sunward direction before perihelion, then the other edge of an identical jet cone on the opposite pole of 3I/ATLAS overlaps with the sunward direction after perihelion.
      As 3I/ATLAS approach perigee on December 19, 2025, the time is ripe to summarize all the anomalies of 3I/ATLAS, organized by themes:
      Geometric Coincidences:
      1. The retrograde trajectory of 3I/ATLAS is aligned to within 5 degrees with the ecliptic plane of the planets around the Sun, with a probability of 0.2% (as discussed here). This suggests that the trajectory may have been planned.
      2. The arrival time of 3I/ATLAS was fine-tuned to bring it to 29 and 54 million kilometers from Mars and Jupiter, respectively, and be unobservable from Earth at perihelion (as discussed here).
      3. The forecasted perijove distance of 3I/ATLAS during its encounter with Jupiter on March 16, 2026 is 53.6 million kilometers, close to Jupiter’s Hill radius, 53.5 million kilometers (as discussed here). This match includes the non-gravitational acceleration that 3I/ATLAS displayed near perihelion. The rare coincidence might mean that 3I/ATLAS intends to release technological devices at Jupiter’s Lagrange points — where fuel requirements are minimal.
      4. Analysis of the Hubble Space Telescope image from July 21, 2025 (as discussed here) suggests that the anti-tail before perihelion must have been in the form of a tightly collimated jet that is about ten times longer than it is wide. This is similar to the tight collimation observed in the latest post-perihelion images. It is difficult to understand how the sublimation of pockets of ice as a result of illumination by sunlight would lead to tightly collimated jets out to a million kilometers. No known comet exhibited a physical sunward jet of this length. For a technological object, a beam of particles might be used to mitigate the risk from the solar wind that would otherwise impact its surface at a relative speed of order 500 kilometers per second and release a hundred thousand times more energy per unit mass than explosives.
      5. At large distances, the rotation axis of 3I/ATLAS was aligned to within 8 degrees with the sunward direction when it entered the solar system (as reported here). The probability for that is 0.5%.
      6. The observed wobble of the pre-perihelion jet in the direction of the Sun (as reported here during July and August 2025) requires the base of the jet to be within 8 degrees from the sun-facing pole, with probability of 0.5%.
      7. The existence of a prominent jet towards the Sun on the way of 3I/ATLAS out of the solar system requires a similar coincidence near the opposite pole of the rotation axis. The fact that a tightly collimated jet appears as the sunward anti-tail both before and after perihelion (while reversing direction at perihelion relative to the direction of motion), has a tiny probability of occurring at random, equal to the square of 0.5% or 0.000025.
      8. The launch base of the post-perihelion anti-tail jet resided on the nightside of 3I/ATLAS before perihelion and the base of the pre-perihelion anti-tail jet is now on the nightside of 3I/ATLAS after perihelion. For these bases to be active only when facing the Sun, they must be well insulated on the nightside for a period longer than several months. However, heat would naturally flow by conduction throughout the body of a natural comet, making this insulation requirement difficult to satisfy.
      9. The gravitational deflection of 3I/ATLAS by 16 degrees at perihelion, is exactly twice the opening angle of the anti-tail jet. This coincidence allows the wobbling jet around the rotation axis to generate an anti-tail in the direction of the Sun before perihelion and a counter jet on the opposite pole after perihelion, with a jet opening angle of 8 degrees on both poles.
      10. 3I/ATLAS arrived from a direction coincident with the radio “Wow! Signal” to within 9 degrees, with a probability of 0.6% (as discussed here).
      Composition Anomalies of the Gas Shed by 3I/ATLAS:
      11. The gas plume surrounding 3I/ATLAS contains much more nickel than iron, as found in industrially-produced nickel alloys, and a nickel to cyanide ratio that is orders of magnitude larger than for thousands of known comets, including 2I/Borisov (see here). This might indicate a technological origin for these abundances.
      12. The gas plume surrounding 3I/ATLAS contains only 4% water by mass, whereas water is a dominant constituent in familiar solar-system comets (as discussed here). The plume might have resulted from the sunlight releasing the ices and dust that accumulated on the surface of a technological object during its journey through cold dense clouds of the interstellar medium.
      Unusual Physical Properties:
      13. The nucleus of 3I/ATLAS is much more massive than 1I/`Oumuamua and 2I/Borisov, while moving faster than both (as discussed here and here). There might not be enough rocky material in interstellar space to deliver a natural iceberg of this mass once per decade to the inner solar system (as discussed here). This suggests that 3I/ATLAS may have targeted the inner solar system rather than being drawn at random from the reservoir of interstellar icebergs.
      14. 3I/ATLAS shows extreme negative polarization, unprecedented for all known comets, including 2I/Borisov (as discussed here). This unusual polarization may be related to its unusual anti-tail.
      15. Near perihelion, 3I/ATLAS brightened faster than any known comet and was bluer than the Sun (as discussed here).
      It is important to keep in mind that other technological civilizations could have used the foundation of a natural object to plant technological devices within it (as discussed here). Whether we encounter a “Trojan Horse” can be decided only through a careful study of the anomalies that distinguish 3I/ATLAS from familiar comets.
      As announced here, the International Asteroid Warning Network is conducting a Planetary Defense campaign to collect as much data as possible on 3I/ATLAS between November 27, 2025 and January 27, 2026. Once this data is made public, I will update my rank for 3I/ATLAS on the Loeb Classification Scale (as quantified here and here). In a new paper that I co-authored with the brilliant PhD student Oem Trivedi (posted today here), we provided the mathematical framework for updating the Loeb scale of interstellar objects over time.
      Irrespective of the true nature of 3I/ATLAS, my New Year’s resolution is simple. Starting on the early morning of December 19, 2025, I will keep looking up in the direction 3I/ATLAS during my future daily jogs before sunrise.
      ABOUT THE AUTHOR
      (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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