{"id":21224,"date":"2025-07-24T19:17:12","date_gmt":"2025-07-24T19:17:12","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/21224\/"},"modified":"2025-07-24T19:17:12","modified_gmt":"2025-07-24T19:17:12","slug":"weighing-interstellar-objects-with-gravitational-wave-detectors-by-avi-loeb-jul-2025","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/21224\/","title":{"rendered":"Weighing Interstellar Objects with Gravitational Wave Detectors | by Avi Loeb | Jul, 2025"},"content":{"rendered":"

\"Avi<\/a>\"\"Image of 3I\/ATLAS taken by the Hubble Space Telescope on July 21, 2025. (Image credit: NASA<\/a>)<\/p>\n

One of the main unknowns concerning interstellar objects, such as 1I\/`Oumuamua<\/a>, 2I\/Borisov<\/a> and 3I\/ATLAS<\/a>, is their mass. In a recent published paper<\/a>, I excluded the possibility that 3I\/ATLAS is an asteroid with a diameter of order 20 kilometers \u2014 as suggested by its high brightness, because detecting such a massive rock over the 5-year observing period of the ATLAS<\/a> telescope is extremely unlikely. On the other hand, I showed that if 3I\/ATLAS has a nucleus with a diameter smaller than 1 kilometer, then its mass would be 8,000 [=(20)\u00b3] times smaller, consistent with the expected reservoir of rocks in interstellar space. In that case, its high brightness is associated with sunlight scattered by the dust cloud surrounding it, an outer halo that carries a small fraction of its mass. If there had been a way of gauging the mass of 3I\/ATLAS, this conjecture could have been tested.<\/p>\n

Can we weigh the mass of interstellar objects? Being able to do so would also allow us to infer their mean mass density based on an independent measurement of their size.<\/p>\n

In a new paper<\/a> that I just wrote with the brilliant graduate student, Valentin Thoss, we studied the possibility of weighing interstellar objects that pass through the inner Solar System using gravitational wave observatories.<\/p>\n

In particular, our paper<\/a> studies the feasibility of probing the gravitational tide from interstellar objects roaming near Earth. Their impulsive gravitational signal is detected as their gravitational tide moves test-masses inside a gravitational wave detector relative to each other. Our calculations assess the ranges of masses, distances and velocities of interlopers to which current and future gravitational wave detectors are sensitive.<\/p>\n

Our paper<\/a> shows that the planned space observatories: Laser Interferometer Space Antenna<\/a> (LISA), Big Bang Observer<\/a> (BBO) and Deci-Hertz Interferometer Gravitational Wave Observatory<\/a> (DECIGO), are sensitive to massive interstellar objects above the scale of 3I\/ATLASS, out to distances of a few million kilometers \u2014 ten times larger than the Earth-Moon separation. The main limitation of each detector is the frequency range to which it is sensitive. In order for an encounter to be detectable, the fly-by must be sufficiently close or fast so that the peak frequency of the gravitational signal, given by the ratio between its relative velocity and distance, matches the frequency window to which the detector is sensitive.<\/p>\n

For illustration, the following figure shows the maximum distance, R, from existing and future gravitational wave detectors, at which a fly-by of an interstellar object of mass, M, is detectable. The plot assumes an object\u2019s velocity of 300 kilometers per second, ten times faster than the orbital speed of the Earth around the Sun or the maximum speed of conventional chemical rockets.<\/p>\n

Zoom image will be displayed\"\"Maximum distance for which gravitational wave detectors are sensitive to a fly-by of a dark interstellar object as a function of its mass of the interstellar object, M, assuming a velocity of 300 kilometers per second.<\/p>\n

The next figure shows the Signal-to-Noise Ratio (SNR) from the closest encounter expected within an observation period of 10 years, assuming that the objects make the dark matter. The SNR is shown for several gravitational wave detectors as a function of the mass, M, and velocity, v, of the objects. The red line indicates the contour for which SNR = 1.<\/p>\n

Zoom image will be displayed\"\"Signal-to-noise ratio (SNR) from the closest encounter expected within an observation time of 10 years, assuming that the objects make up the dark matter. The SNR is shown for several gravitational wave detectors as a function of the mass, M, and velocity, v, of the dark interstellar objects. The red line indicates the contour for which SNR = 1.<\/p>\n

The likelihood for DECIGO to detect at least one event from the fly-by of compact objects, depends on their individual masses and their total local mass density in the Milky-Way. The next figure assumes an observation time of 10 years and random orbits for interstellar objects. The red shaded band corresponds to the range of the latest observational estimates of the local dark matter density. The dotted line indicates the contour of 50% detection probability, for a reduction in the expected detector noise level by a factor of 2.<\/p>\n

Zoom image will be displayed\"\"Likelihood for DECIGO to detect at least one event from the fly-by of compact objects, shown as a function of their mass, M, and local mass density in the Milky-Way, \u03c1, assuming an observation period of 10 years. The red shaded band corresponds to the range of the latest observational estimates for the local dark matter density. The dotted line indicates the contour of 50% detection probability, for a reduction in the detector noise level by a factor of two.<\/p>\n

In summary, our new paper<\/a> finds that if the solar system encounters dark interstellar objects with the cumulative mass density of dark matter, then future gravitational wave observatories such as DECIGO offer good prospects for detecting them in the mass window of 10\u2013100,000 tons.<\/p>\n

Obviously, the most interesting class of dark interstellar objects would be stealth spacecraft employed by extraterrestrial civilizations, in the style of our B-2 Spirit aircraft<\/a>, to avoid detection by telescopes which rely on the reflection of sunlight from their surface. These low-albedo objects might have an unexpected appearance rate in the inner solar system if their trajectories are designed to target the habitable planets around the Sun \u2014 where the \u201cparty\u201d of life-as-we-know-it takes place.<\/p>\n

Gladly, gravity cannot be screened and even these stealth objects would be detectable by future gravitational wave observatories if their masses and velocities are large enough and their distance of closest approach is short enough. In that case, each data analyst working on future gravitational wave observatories could say: \u201cDark interstellar objects \u2014 go ahead, make my day!\u201d<\/p>\n

ABOUT THE AUTHOR<\/p>\n

Zoom image will be displayed\"\"(Image Credit: Chris Michel, National Academy of Sciences, 2023)<\/p>\n

Avi Loeb is the head of the Galileo Project, founding director of Harvard University\u2019s \u2014 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\u20132020). He is a former member of the President\u2019s 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 \u201cExtraterrestrial:<\/a> The First Sign of Intelligent Life Beyond Earth<\/a>\u201d and a co-author of the textbook \u201cLife in the Cosmos<\/a>\u201d, both published in 2021. The paperback edition of his new book, titled \u201cInterstellar<\/a>\u201d, was published in August 2024.<\/p>\n","protected":false},"excerpt":{"rendered":"Image of 3I\/ATLAS taken by the Hubble Space Telescope on July 21, 2025. (Image credit: NASA) One of…\n","protected":false},"author":2,"featured_media":21225,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,314,66],"class_list":{"0":"post-21224","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-ca","9":"tag-canada","10":"tag-physics","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/21224","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=21224"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/21224\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/21225"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=21224"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=21224"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=21224"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}