August 9, 2022

Largest neutron star to date is a ‘black widow’ eating its mate

Weighing this record-setting neutron star, which best the charts at 2 . 35 times the bulk of the sun, helps astronomers understand the weird quantum state of matter inside these types of dense objects

A dense, collapsed star spinning 707 times per second— making it one of the fastest spinning ungeladenes nukleon stars in the Milky Method galaxy— has shredded and consumed nearly the entire bulk of its stellar companion and, in the process, grown into the largest neutron star observed to date.

Evaluating this record-setting  neutron   star, which tops the charts on 2 . 35 times the  mass   of the sun, helps astronomers understand the weird quantum state of matter inside these dense objects, which— if they get much heavier than that— collapse entirely plus disappear as a black hole.

“ We all know roughly how matter reacts at nuclear densities, similar to the nucleus of a uranium atom, ” said Alex Filippenko, Distinguished Professor of Astronomy at the University of California, Berkeley. “ A neutron star is like one giant nucleus, but when you have one-and-a-half solar masses of these things, which is about 500, 1000 Earth masses of nuclei just about all clinging together, it’s not whatsoever clear how they will behave. ”

Roger W. Romani, professor of astrophysics at Stanford University or college, noted that neutron superstars are so dense— 1 cu inch weighs over 10 billion tons— that their particular cores are the densest matter in the universe short of  black holes , which because they are hidden behind their event horizon are impossible to study. The neutron star, a pulsar designated PSR J0952-0607, is hence the densest object inside sight of Earth.

The measurement of the neutron star’s mass had been possible thanks to the extreme awareness of the 10-meter Keck We telescope on Maunakea within Hawai’i, which was just capable of record a spectrum of visible light from the hotly glowing companion star, right now reduced to the size of the large gaseous planet. The stars are about a few, 000 light years through Earth in the direction of the constellation Sextans.

Discovered in 2017 , PSR J0952-0607 is referred to as a “ black widow” pulsar— an analogy to the tendency associated with female black widow spiders to consume the much smaller male after mating. Filippenko and Romani have been studying dark widow systems for more than a decade, hoping to establish top of the limit on how large ungeladenes nukleon stars/pulsars can grow.

“ By combining this measurement with those of several other black widows, we show that neutron stars must reach at least this particular mass, 2 . 35 plus or minus 0. 17 solar masses, ” mentioned Romani, who is a professor of physics in Stanford’s School of Humanities plus Sciences and member of the particular Kavli Institute for Particle Astrophysics and Cosmology. “ In turn, this provides some of the strongest constraints on the property associated with matter at several times the density seen in atomic nuclei. Indeed, many otherwise popular models of dense-matter physics are excluded by this outcome. ”

If 2 . 35 solar people is close to the  upper limit   of neutron stars, the researchers say, then the inner surface is likely to be a soup associated with neutrons as well as up and down quarks— the constituents of normal protons and neutrons— although not exotic matter, such as “ strange” quarks or kaons, which are particles that contain a strange quark.

“ A high maximum mass designed for neutron stars suggests that it is a mixture of nuclei and their own dissolved up and down quarks entirely to the core, ” Romani said. “ This excludes many proposed states of matter, especially those with exotic interior composition. ”

Romani, Filippenko and Stanford graduate student Dinesh Kandel are co-authors of a paper describing the team’s results that has been accepted regarding publication by  The particular Astrophysical Journal Letters .

How big can they grow?

Astronomers generally agree that when a star having a core larger than about 1 ) 4 solar masses collapses at the end of its life, this forms a dense, small object with an interior below such high pressure that all atoms are smashed together to form a sea of neutrons plus their subnuclear constituents, quarks. These neutron stars are usually born spinning, and though too dim to be seen in noticeable light, reveal themselves because pulsars, emitting beams associated with light— radio waves, X-rays or even gamma rays— that flash Earth as they spin, much like the rotating beam of the lighthouse.

“ Ordinary” pulsars spin plus flash about once per second, on average, a swiftness that can easily be explained given the normal rotation of the star before it collapses. But some pulsars repeat 100s or up to 1, 000 times per second, that is hard to explain unless issue has fallen onto the neutron star and unique it up. But for some  millisecond pulsars , no companion is visible.

One possible explanation meant for isolated millisecond pulsars is that each did once have a companion, but it stripped it down to nothing.

“ The evolutionary pathway is absolutely fascinating. Double affirmation point, ” Filippenko mentioned. “ As the companion star evolves and starts becoming a red giant, material spills over to the neutron superstar, and that spins up the neutron star. By spinning upward, it now becomes extremely energized, and a wind associated with particles starts coming out through the neutron star. That breeze then hits the subscriber star and starts burning material off, and as time passes, the donor star’s bulk decreases to that of a planet, and if even more time passes, it disappears altogether. Therefore , that’s how lone millisecond pulsars could be formed. These people weren’t all alone to begin with— they had to be in a binary pair— but they gradually evaporated away their companions, and today they’re solitary. ”

The pulsar PSR J0952-0607 and its faint partner star support this origin story for millisecond pulsars.

“ These types of planet-like objects are the dregs of normal stars that have contributed mass and angular momentum, spinning up their particular pulsar mates to nanosecond periods and increasing their own mass in the process, ” Romani said.

“ In a case of cosmic ingratitude, the black widow pulsar, which has devoured a large part of its mate, today heats and evaporates the companion down to planetary world and perhaps complete annihilation, ” said Filippenko.

Spider pulsars include redbacks and tidarrens

Finding dark widow pulsars in which the friend is small, but not too small to detect, any of few ways to consider neutron stars. In the case of this particular binary system, the companion star— now only twenty times the mass of Jupiter— is distorted by the mass of the neutron superstar and tidally locked, just like the way our moon is certainly locked in orbit to ensure that we see only one part. The neutron star-facing side is heated to temperature ranges of about 6, 200 Kelvin, or 10, 700 levels Fahrenheit, a bit hotter compared to our sun, and just bright enough to see with a  large telescope .

Filippenko and Romani turned the Keck I telescope on PSR J0952-0607 on six events over the last four years, each time observing with the Low Resolution Imaging Spectrometer in 15-minute chunks to catch the faint companion at particular points in its 6. 4-hour orbit of the pulsar. Simply by comparing the spectra to that particular of similar sun-like celebrities, they were able to measure the orbital velocity of the  companion star   and calculate the mass of the neutron star.

Filippenko and Romani have examined about a number of black widow systems up to now, though only six got companion stars bright sufficient to let them calculate the mass. All involved ungeladenes nukleon stars less massive than the  pulsar   PSR J0952-060. Most are hoping to study more black widow pulsars, as well as their own cousins: redbacks, named for the Australian equivalent of dark widow pulsars, which have buddies closer to one-tenth the  mass of the sun ; and what Romani dubbed tidarrens— where the companion is around one-hundredth of a solar mass— after a relative of the  black widow   spider. The male of this species, Tidarren sisyphoides, is about 1% of the female’s size.

“ We can keep looking for black widows and similar  neutron stars   that skate even closer to the particular black hole brink. When we don’t find any kind of, it tightens the argument that 2 . 3  solar masses   is the true limit, outside of which they become  dark holes , ” Filippenko said.

“ This is right at the limit of what the Keck telescope can do, so barring excellent observing conditions, tightening the measurement of PSR J0952-0607 likely awaits the 30-meter telescope era, ” added Romani.

Some other co-authors of the ApJ Letters paper are UC Berkeley researchers Thomas Brink plus WeiKang Zheng.

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