Mountains on neutron stars are not even a millimetre tall due to extreme gravity

According to simulations, anyway


The gravitational field of neutron stars is so strong that so-called mountains poking out from their surfaces only grow to a fraction of a millimetre in height in simulations.

When certain massive stars finish burning all their fuel and go supernova, the leftover core matter collapses in on itself to form a neutron star. These bodies are compressed to such a degree that their electrons and protons combine into neutrons. Their mass – typically about 1.4 times the mass of our Sun – is squeezed into a sphere just 20km or so across. Our star has a diameter of 1.4 million km, for comparison.

Neutron stars are thus among the densest objects in the known universe, and have extreme gravitational fields, so much so that mountains on their surfaces may only be a fraction of a millimetre tall. This would make their surface smoother and more uniform than previously thought, according to Nils Andersson, professor of applied mathematics at England's University of Southampton. These conclusions were presented this week at 2021's National Astronomy Meeting hosted by the Royal Astronomical Society.

“Colloquially, 'mountain' is taken to mean 'quadrupole deformation,' basically stretching a spinning star in such a way that it becomes optimal at emitting gravitational waves,” Prof Andersson explained to The Register. “Perhaps the word is also ironic given that these 'mountains’ are tiny."

The gravitational wave aspect is interesting. Spinning neutron stars should produce these waves, which are basically ripples in the fabric of spacetime, from their surface deformations. If neutron stars' mountains, if you will, truly are so small, it may be more difficult than some anticipate to detect their gravitational waves.

Unlike mountains on Earth, these minuscule structures on neutron stars aren’t formed by geological processes. Instead, mountains on these dead stars are forged by how much material is pulled outward when they spin. It doesn’t stretch by much since the star's gravity crushes it inwards.

“First of all, one would never expect these mountains to be huge, given that the gravity on a neutron star is so strong," the professor added. "But if you compare the relative change in the gravitational potential then the predicted neutron star mountains would no longer be so puny compared to, say, Mount Everest."

Since the 2000s, at least, scientists have been trying to figure out what's going on at the surface of neutron stars. Prof Andersson and his colleagues emitted two papers this year and last describing computer models that aim to predict neutron stars' mountain heights; these simulate the objects as bodies of dense fluid contained in an elastic crust.

“These results show how neutron stars truly are remarkably spherical objects,” said co-author Fabian Gittins, a PhD student in theoretical astrophysics at Southampton. “Additionally, they suggest that observing gravitational waves from rotating neutron stars may be even more challenging than previously thought.”

Gravitational-wave detectors like LIGO and Virgo have spotted ripples of spacetime caused by pairs of neutron stars smashing into one another; we've yet to see waves from a lone spinning neutron star. And if these surface simulations are correct, that may not be a surprise. ®

Similar topics


Other stories you might like

  • Stolen university credentials up for sale by Russian crooks, FBI warns
    Forget dark-web souks, thousands of these are already being traded on public bazaars

    Russian crooks are selling network credentials and virtual private network access for a "multitude" of US universities and colleges on criminal marketplaces, according to the FBI.

    According to a warning issued on Thursday, these stolen credentials sell for thousands of dollars on both dark web and public internet forums, and could lead to subsequent cyberattacks against individual employees or the schools themselves.

    "The exposure of usernames and passwords can lead to brute force credential stuffing computer network attacks, whereby attackers attempt logins across various internet sites or exploit them for subsequent cyber attacks as criminal actors take advantage of users recycling the same credentials across multiple accounts, internet sites, and services," the Feds' alert [PDF] said.

    Continue reading
  • Big Tech loves talking up privacy – while trying to kill privacy legislation
    Study claims Amazon, Apple, Google, Meta, Microsoft work to derail data rules

    Amazon, Apple, Google, Meta, and Microsoft often support privacy in public statements, but behind the scenes they've been working through some common organizations to weaken or kill privacy legislation in US states.

    That's according to a report this week from news non-profit The Markup, which said the corporations hire lobbyists from the same few groups and law firms to defang or drown state privacy bills.

    The report examined 31 states when state legislatures were considering privacy legislation and identified 445 lobbyists and lobbying firms working on behalf of Amazon, Apple, Google, Meta, and Microsoft, along with industry groups like TechNet and the State Privacy and Security Coalition.

    Continue reading
  • SEC probes Musk for not properly disclosing Twitter stake
    Meanwhile, social network's board rejects resignation of one its directors

    America's financial watchdog is investigating whether Elon Musk adequately disclosed his purchase of Twitter shares last month, just as his bid to take over the social media company hangs in the balance. 

    A letter [PDF] from the SEC addressed to the tech billionaire said he "[did] not appear" to have filed the proper form detailing his 9.2 percent stake in Twitter "required 10 days from the date of acquisition," and asked him to provide more information. Musk's shares made him one of Twitter's largest shareholders. The letter is dated April 4, and was shared this week by the regulator.

    Musk quickly moved to try and buy the whole company outright in a deal initially worth over $44 billion. Musk sold a chunk of his shares in Tesla worth $8.4 billion and bagged another $7.14 billion from investors to help finance the $21 billion he promised to put forward for the deal. The remaining $25.5 billion bill was secured via debt financing by Morgan Stanley, Bank of America, Barclays, and others. But the takeover is not going smoothly.

    Continue reading

Biting the hand that feeds IT © 1998–2022