First Discovery of a Magnetar’s Birth May Not Explain All Fast Radio Bursts
What would be the flagship signature of a very advanced, ambitious civilization?
One possibility is the technology to propel a spacecraft the size of New-York City along with its population of ten million residents to the speed of light over a period of about a year. This requires an average acceleration of 1 gee, similar to the surface gravity of Earth. The acceleration phase would feel like living on the surface of Earth, as according to Albert Einstein’s theory of General Relativity — there is no fundamental difference between an artificially-induced acceleration and gravitational acceleration. Keep in mind that an observer within a free-falling elevator feels no gravity whatsoever.
How can we drive roughly a million tons to the speed of light in one year? A simple technology that can accomplish that challenge is light sails. An Earth-size membrane, illuminated by a radio transmitter that harvests the total power of starlight on the surface of a habitable Earth-like planet, could carry this massive payload up to the speed of light over a period of a year. The optimal radio frequency to keep the light beam focused on the sail during the acceleration period is of order 1 gigahertz.
Given the motion of this narrow radio beam in our sky, this system would generate a fast radio burst (FRB) that lasts a thousandth of a second (millisecond) for a launch system at a cosmological distance of the order of billions of light years. The brightness of the FRB would be roughly about 1 Jansky. As it turns out, several thousand FRBs with millisecond duration and this brightness were detected at cosmological distances.
Could some of them be related to advanced technological civilizations? I raised this possibility in a paper that I published here in March 2017, with my then-postdoc, Manasvi Lingam. The publication date was seven months before the first interstellar object 1I/`Oumuamua was discovered, exhibiting a flat geometry as well as a non-gravitational acceleration that declines inversely with the square of its distance from the Sun, as expected from a light-sail. I therefore suggested that `I/`Oumuamua might be a light-sail (here) or a broken piece of a thin Dyson sphere (here) .
The light-sail conjecture for FRBs was sidelined and replaced by the popular hypothesis that the sources of these bright radio transients are relatives of fainter radio sources, called pulsars, which are routinely discovered in the Milky-Way galaxy. Pulsars are rotating neutron stars, relic from the collapse of the cores of stars more massive than 8 solar masses, after they consume their nuclear fuel. A neutron star typically packs 1.4 solar masses within a radius of 12 kilometers, about half the length of Manhattan Island. If its rotation axis is misaligned with its magnetic axis which beams radio waves, it appears as a pulsating lighthouse as the radio beam crosses our line-of-sight, hence the name pulsar. As of a result of their energy loss, pulsars spin down with the product of the spin-down rate scaling as the square of the magnetic field strength.
Typical pulsars display a magnetic field of up to a trillion (10^{12}) Gauss (equivalent to a hundred million Tesla), but some rare neutron stars show evidence for a magnetic field which is up to a thousand times larger. These are called magnetars. The popular view is that FRBs originate from the powerful radio beams emitted by magnetars and none are related to alien civilizations.
Pulsars are born when the core of a massive star bounces, leading to the ejection of the envelope of the star. The energy released in the bounce is comparable to the gravitational binding energy of the relic neutron star, and typically 99% of it is carried by neutrinos — weakly interacting particles that escape relatively easily from the collapsed core. The remaining 1% drives an explosion — called a supernova — which disperses the debris of the stellar envelope into the surrounding interstellar medium and enriches it with the heavy elements that were cooked inside nuclear furnace of the progenitor star. Most of the weight of our body comes from oxygen and carbon that were produced by nearby supernovae.
Some supernovae appear to be an order of magnitude more luminous than typical supernovae, and are therefore labeled as superluminous supernova. A new paper that was just published in Nature magazine here, reports the discovery of a periodic modulation in the lightcurve of a superluminous supernova. The modulation is naturally explained by the wobble of an accretion disk around a newly-formed magnetar. The measured spin period of 4.2 (± 0.2) millisecond and the inferred spindown rate are consistent with a magnetic field of a hundred trillion (10^{14}) Gauss (equivalent to ten billion Tesla). This constitutes the first discovery of the birth of a magnetar.
We now know how some magnetars can be born with the necessary spin period and magnetic field to produce FRBs. But are all FRBs associated with young magnetars?
Certainly not. Massive stars are short lived and so we expect magnetars to be born in young, star forming environments. However, we know that a subset of FRBs — represented for example by FRB 20240209A (reported here), reside in old, quiescent elliptical galaxies. This finding challenges the assumption that FRBs only originate from magnetars formed in young, star-forming regions.
Science is fun when treated as a learning experience. It is based on the humility to learn, not the arrogance of expertise.
***
Before my morning jog at sunrise, I received the following uplifting message:
“Dear Professor Loeb,
I have been following your work for some time. Even as a non-scientist, I feel deeply moved and inspired by what I sense you are trying to do — both within your scientific vision and in the invitation that you extend to those willing to listen.
In your recent talks I sensed something very sincere: an open call to curiosity, to wonder, and to the courage of asking questions before we have answers. That invitation inspired the small visual poem I am sending you.
Please accept it simply as a humble gesture of participation in what I perceive as your call to a science that remains profoundly human.
For context, I am a poet. I recently published a book written in dialogue with an artificial intelligence — not as a tool, but as a respectful collaboration with what one might almost call an alien form of intelligence.
The image accompanying the poem was generated in that same spirit by the AI that collaborated with me.
Thank you for the curiosity and intellectual courage you bring to the public conversation about science.
Warm regards,
Andrea Fassone
In the House of θαυμάζειν
… it moves
still and
out of sync
yet in unison
through singularity
that feeling
is too little
of measure
and suspension
memore
beyond time
to nothing before
nor after
it aches
that something
behind
the stone cast
and me
who watches…
AF — IN MEDIA VIA”
ABOUT THE AUTHOR
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
