From McGill University: “Glitch in Neutron Star Reveals Its Hidden Secrets”

McGill University

From McGill University

12 Aug 2019

Contact:
Cynthia Lee
Senior Communications Officer, Media Relations, McGill
cynthia.lee@mcgill.ca
514-398-6754

Neutron stars are not only the densest objects in the Universe, they also rotate very fast and regularly. Until they suddenly don’t.

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If parts of the neutron star interior start to move outwards, the star spins faster. This is called a “glitch,” and it’s providing astronomers with a brief insight into what lies within these mysterious objects.

In a paper published August 12 in the journal Nature Astronomy, a team from Monash University in Melbourne, the Australian Research Council’s Centre of Excellence for Gravitational Wave Discovery (OzGrav), McGill University, and the University of Tasmania, studied a neutron star known as the Vela Pulsar. Located in the southern sky, and approximately 1,000 light years from Earth, the Vela Pulsar is known to glitch about once every three years. Only five percent of pulsars glitch, so the Vela Pulsar’s regularity has made it a favourite of glitch hunters.

By reanalysing data from the 2016 Vela glitch, taken by co-author Jim Palfreyman from the University of Tasmania, the team found that the glitching star started spinning faster than previously observed, before relaxing down to a final state.

According to Paul Lasky from Monash University, this observation gives scientists the first-ever detailed glimpse into the interior of the star – revealing that the inside actually has three different components.

“One of these components, a soup of superfluid neutrons in the inner layer of the crust, moves outwards first and hits the rigid outer crust of the star, causing it to spin up,” says Lasky. “But then, a second soup of superfluid that moves in the core catches up to the first, causing the spin of the star to slow back down.”

This overshoot has been predicted by researchers—including study co-author Vanessa Graber from McGill University, who visited the Monash team as an OzGrav International Visitor at the end of last year–but had never been observed until now.

One glitching mystery, however, has led to another. “Immediately before the glitch, we noticed that the star seems to slow down its rotation rate before spinning back up,” says the study’s first author, Greg Ashton from the Monash School of Physics and Astronomy. “We actually have no idea why this is, and it’s the first time it’s ever been seen! We speculate it’s related to the cause of the glitch, but we’re honestly not sure,” he said adding that he suspects this new paper to spur some new theories on neutron stars and glitches.

See the full article here .

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With some 300 buildings, more than 38,500 students and 250,000 living alumni, and a reputation for excellence that reaches around the globe, McGill has carved out a spot among the world’s greatest universities.
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#astronomy, #astrophysics, #basic-research, #cosmology, #mcgill-university, #neutron-stars, #vela-pulsar

From Medium: “IGR J18245–2452: The most important neutron star you’ve never heard of”

From Medium

Jan 21, 2019
Graham Doskoch

Astronomers have spent thirty years on the theory behind how millisecond pulsars form. Now we know they got it right.

Neutron stars are known for their astonishing rotational speeds, with most spinning around their axes many times each second. The mechanism behind this is simple: When a fairly massive star several times the radius of the Sun collapses into a dense ball about ten kilometers in diameter, conservation of angular momentum dictates that it must spin quicker.

However, one class of neutron stars can’t be explained this way: millisecond pulsars. These exotic objects spin hundreds of times each second, with the fastest, PSR J1748–2446ad, rotating at over 700 Hertz! Since their discovery in the 1980s, a slightly different evolutionary path has been proposed. After studying dozens of systems, astronomers theorized that millisecond pulsars are very old — old enough that they’ve lost much of their original angular momentum to radiation. However, they’re also in binary systems, and under certain conditions, a companion star can transfer matter — and thus angular momentum — to the pulsar, spinning it back up again.

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A plot of the periods and magnetic fields of pulsars. Millisecond pulsars have extremely short periods, and comparatively weak magnetic fields. Image credit: Swinburne University of Technology

During this period of accretion, the system should become an x-ray binary, featuring strong emission from the hot plasma in the neutron star’s accretion disk. There should also be periods where the neutron star behaves like an ordinary radio pulsar, emitting radio waves we can detect on Earth. If we could detect both types of radiation from a single system, it might be the clinching bit of evidence for the spin-up model of millisecond pulsar formation.

In 2013, astronomers discovered just that: a binary system known as IGR J18245–2452 from its x-ray outbursts, and PSR J1824–2452I for its radio emissions. First observed in 2008, it had exhibited both radio pulsations and x-ray outbursts within a short period of time, clear evidence of the sort of transitional stage everyone had been looking for. This was it: a confirmation of the ideas behind thirty years of work on how these strange systems form.

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INTEGRAL observations of IGR J18245–2452 from February 2013 (top) and March/April 2013 (bottom). The system is only visible in x-rays in the second period. Image credit: ESA/INTEGRAL/IBIS/Jörn Wilms.

ESA/Integral

The 2013 outburst

Towards the end of March of 2013, the INTEGRAL and Swift space telescopes detected x-rays from an energetic event coming from the core of the globular cluster M28 (Papitto et al. 2013).

NASA Neil Gehrels Swift Observatory

It appeared to be an outburst of some kind — judging by the Swift observations, likely a thermonuclear explosion. A number of scenarios can lead to x-ray transients, including novae and certain types of supernovae. Binary systems are often the culprits, where mass can be transferred from one star or compact object to another.

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Fig. 7, Papitto et al. Swift data from observations of an outburst show its characteristic exponentially decreasing cooling.

One thermonuclear burst observed by Swift followed a time evolution profile expected for such a detonation: An increase in luminosity for 10 seconds, followed by an exponential decrease with a time constant of 38.9 seconds. This decrease represents the start of post-burst cooling. The other outbursts from the system should have had similar profiles characteristic of x-ray-producing thermonuclear explosions, and indeed later observations of the system have confirmed that this is indeed the case (De Falco et al. 2017 [Astronomy and Astrophysics]), albeit with slightly different rise times and decay constants.

To determine the identity of the transient, now designated IGR J18245–2452, astronomers made follow-up observations using the XMM-Newton telescope.

ESA/XMM Newton

The nature of the outburst would determine how it evolved over time. For instance, supernovae (usually) decrease in brightness over the course of weeks or months. In this case, however, the x-rays were still detected — albeit a bit weaker. More surprisingly, the strength of the emission appeared to be modulated, varying with a period of 3.93 milliseconds.

Such a short period seemed to indicate that a pulsar might be responsible. The team checked databases of known radio pulsars and found one that matched the x-ray source: PSR J1824–2452I, a millisecond pulsar in a binary system. Even after this radio counterpart had been found, however, two questions remained: Were these x-ray pulses new or a long-term process, and how did they relate to the radio emission?

Diving into the archives

A handy tool for observational astronomers is archival images. By looking at observations taken months, years or decades before an event, scientists can — if they’re lucky — peek into the past to see what an object of interest looked like long before it became interesting. Archival data is often of use for teams studying supernovae, as even a previously uninteresting or unnoticed star can tell the story of a supernova’s progenitor.

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Fig. 3, Papitto et al. Chandra images from 2008, showing the system in quiescent (top) and active (bottom) states.

NASA/Chandra X-ray Telescope

In this case, Papitto et al. looked at Chandra observations from 2008, comparing them with new data from April 2013. They found x-ray variability occurring shortly after a period of radio activity by the pulsar, indicating that the system had switched off its radio emissions and started emitting x-rays. This was extremely interesting, because new observations with three sensitive radio telescopes — Green Bank, Parkes, and Westerbork — indicated that the pulsar was no longer active in radio waves.

Green Bank Radio Telescope, West Virginia, USA, now the center piece of the GBO, Green Bank Observatory, being cut loose by the NSF

CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

Westerbork Synthesis Radio Telescope, an aperture synthesis interferometer near World War II Nazi detention and transit camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands

It was possible that the pulsar had been eclipsed and emission was ongoing, and this may indeed have happened at some points, but was not likely to be the main factor behind the apparent quiescence.

A few weeks later, however, the exact opposite happened: the pulsar exited its quiescent radio state and was again picked up by the three radio telescopes. In short, over a period of months, it had oscillated between behaving like an x-ray binary and a normal millisecond pulsar. Finally, x-ray observations had conclusively shown that this sort of bizarre transitional state was possible!

The mechanism

IGR J18245–2452 spends the vast majority of its time in what is known as a “quiescent” state, during which there is comparatively little x-ray activity. The pulsar’s magnetosphere exerts a pressure on the infalling gas, forming a disk at a suitable distance from the surface. Eventually, however, there is enough buildup that an x-ray outburst occurs, lasting for a few months. The outburst decreases the mass accretion rate, and the magnetosphere pushes away much of the transferred gas, allowing radio pulsations to take place once more.

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Fig. 2, De Falco et al. Over a period of a few weeks, IGR J18245–2452 underwent a number of individual x-ray outbursts, themselves indicative of a brief period of x-ray activity and radio silence.

It’s expected that the pulsar will eventually be spun-up until its rotational period is on the order of a millisecond or so. It will cease x-ray emissions, and be visible mainly through radio pulses. All of this, however, is far in the future, and during our lifetimes, IGR J18245–2452 will stay in its current transitional state, halfway between an x-ray binary and a millisecond pulsar.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

See the full article here .

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About Medium

Medium is an online publishing platform developed by Evan Williams, and launched in August 2012. It is owned by A Medium Corporation. The platform is an example of social journalism, having a hybrid collection of amateur and professional people and publications, or exclusive blogs or publishers on Medium, and is regularly regarded as a blog host.

Williams developed Medium as a way to publish writings and documents longer than Twitter’s 140-character (now 280-character) maximum.

#astronomy, #astrophysics, #basic-research, #cosmology, #first-observed-in-2008-a-binary-system-known-as-igr-j18245-2452-from-its-x-ray-outbursts-and-psr-j1824-2452i-for-its-radio-emissions, #medium, #millisecond-pulsars, #neutron-stars, #supernovae, #the-fastest-millisecond-pulsar-psr-j1748-2446ad

From Caltech: “Magnetar Mysteries in our Galaxy and Beyond”

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From Caltech

01/09/2019

Whitney Clavin
(626) 395-1856
wclavin@caltech.edu

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Illustration of a magnetar—a rotating neutron star with incredibly powerful magnetic fields.
Credit: NASA/CXC/M.Weiss

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The 70-meter radio dish (DSS-43) in Canberra, Australia, part of NASA’s Deep Space Network.
Credit: NASA/DSN

New research looks at possible links between magnetars and extragalactic radio bursts.

In a new Caltech-led study, researchers from campus and the Jet Propulsion Laboratory (JPL) have analyzed pulses of radio waves coming from a magnetar—a rotating, dense, dead star with a strong magnetic field—that is located near the supermassive black hole at the heart of the Milky Way galaxy. The new research provides clues that magnetars like this one, lying in close proximity to a black hole, could perhaps be linked to the source of “fast radio bursts,” or FRBs. FRBs are high-energy blasts that originate beyond our galaxy but whose exact nature is unknown.

“Our observations show that a radio magnetar can emit pulses with many of the same characteristics as those seen in some FRBs,” says Caltech graduate student Aaron Pearlman, who presented the results today at the 233rd meeting of the American Astronomical Society in Seattle. “Other astronomers have also proposed that magnetars near black holes could be behind FRBs, but more research is needed to confirm these suspicions.”

The research team was led by Walid Majid, a visiting associate at Caltech and principal research scientist at JPL, which is managed by Caltech for NASA, and Tom Prince, the Ira S. Bowen Professor of Physics at Caltech. The team looked at the magnetar named PSR J1745-2900, located in the Milky Way’s galactic center, using the largest of NASA’s Deep Space Network radio dishes in Australia. PSR J1745-2900 was initially spotted by NASA’s Swift X-ray telescope, and later determined to be a magnetar by NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), in 2013.

NASA Neil Gehrels Swift Observatory

NASA NuSTAR X-ray telescope

“PSR J1745-2900 is an amazing object. It’s a fascinating magnetar, but it also has been used as a probe of the conditions near the Milky Way’s supermassive black hole,” says Fiona Harrison, the Benjamin M. Rosen Professor of Physics at Caltech and the principal investigator of NuSTAR. “It’s interesting that there could be a connection between PSR J1745-2900 and the enigmatic FRBs.”

Magnetars are a rare subtype of a group of objects called pulsars; pulsars, in turn, belong to a class of rotating dead stars known as neutron stars. Magnetars are thought to be young pulsars that spin more slowly than ordinary pulsars and have much stronger magnetic fields, which suggests that perhaps all pulsars go through a magnetar-like phase in their lifetime.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

The magnetar PSR J1745-2900 is the closest-known pulsar to the supermassive black hole at the center of the galaxy, separated by a distance of only 0.3 light-years, and it is the only pulsar known to be gravitationally bound to the black hole and the environment around it.

In addition to discovering similarities between the galactic-center magnetar and FRBs, the researchers also gleaned new details about the magnetar’s radio pulses. Using one of the Deep Space Network’s largest radio antennas, the scientists were able to analyze individual pulses emitted by the star every time it rotated, a feat that is very rare in radio studies of pulsars. They found that some pulses were stretched, or broadened, by a larger amount than predicted when compared to previous measurements of the magnetar’s average pulse behavior. Moreover, this behavior varied from pulse to pulse.

“We are seeing these changes in the individual components of each pulse on a very fast time scale. This behavior is very unusual for a magnetar,” says Pearlman. The radio components, he notes, are separated by only 30 milliseconds on average.

One theory to explain the signal variability involves clumps of plasma moving at high speeds near the magnetar. Other scientists have proposed that such clumps might exist but, in the new study, the researchers propose that the movement of these clumps may be a possible cause of the observed signal variability. Another theory proposes that the variability is intrinsic to the magnetar itself.

“Understanding this signal variability will help in future studies of both magnetars and pulsars at the center of our galaxy,” says Pearlman.

In the future, Pearlman and his colleagues hope to use the Deep Space Network radio dish to solve another outstanding pulsar mystery: Why are there so few pulsars near the galactic center? Their goal is to find a non-magnetar pulsar near the galactic-center black hole.

“Finding a stable pulsar in a close, gravitationally bound orbit with the supermassive black hole at the galactic center could prove to be the Holy Grail for testing theories of gravity,” says Pearlman. “If we find one, we can do all sorts of new, unprecedented tests of Albert Einstein’s general theory of relativity.”

The new study, titled, “Pulse Morphology of the Galactic Center Magnetar PSR J1745-2900,” appeared in the October 20, 2018, issue of The Astrophysical Journal and was funded by a Research and Technology Development grant through a contract with NASA; JPL and Caltech’s President’s and Director’s Fund; the Department of Defense; and the National Science Foundation. Other authors include Jonathon Kocz of Caltech and Shinji Horiuchi of the CSIRO (Commonwealth Scientific and Industrial Research Organization) Astronomy & Space Science, Canberra Deep Space Communication Complex.

See the full article here .


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The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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Caltech campus

#astronomy, #astrophysics, #basic-research, #caltech, #cosmology, #frbs-fast-radio-bursts-one-of-todays-big-mysteries-in-astronomy, #neutron-stars, #pulsars, #radio-magnetars, #the-team-looked-at-the-magnetar-named-psr-j1745-2900-located-in-the-milky-ways-galactic-center-using-the-largest-of-nasas-deep-space-network-radio-dishes-in-australia

From European Space Agency: “ESA sets clock by distant spinning stars”

ESA Space For Europe Banner

From European Space Agency

24 December 2018

ESA’s technical centre in the Netherlands has begun running a pulsar-based clock. The ‘PulChron’ system measures the passing of time using millisecond-frequency radio pulses from multiple fast-spinning neutron stars.

Operating since the end of November, this pulsar-based timing system is hosted in the Galileo Timing and Geodetic Validation Facility of ESA’s ESTEC establishment, at Noordwijk in the Netherlands, and relies on ongoing observations by a five-strong array of radio telescopes across Europe.

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Pulsar encased in supernova bubble

Neutron stars are the densest form of observable matter in the cosmos, formed out of the collapsed core of exploding stars. Tiny in cosmic terms, on the order of a dozen kilometres in diameter, they still have a higher mass than Earth’s Sun.

A pulsar is a type of rapidly rotating neutron star with a magnetic field that emits a beam of radiation from its pole. Because of their spin – kept steady by their extreme density – pulsars as seen from Earth appear to emit highly regular radio bursts – so much so that in 1967 their discoverer, UK astronomer Jocelyn Bell Burnell, initially considered they might be evidence of ‘little green men’.

Women in STEM – Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

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ESTEC

“PulChron aims to demonstrate the effectiveness of a pulsar-based timescale for the generation and monitoring of satellite navigation timing in general, and Galileo System Time in particular,” explains navigation engineer Stefano Binda, overseeing the PulChron project.

“A timescale based on pulsar measurements is typically less stable than one using atomic or optical clocks in the short term but it could be competitive in the very long term, over several decades or more, beyond the working life of any individual atomic clock.

“In addition, this pulsar time scale works quite independently of whatever atomic clock technology is employed – it doesn’t rely on switches between atomic energy states but the rotation of neutron stars.”

PulChron sources batches of pulsar measurements from the five 100-m class radio telescopes comprising the European Pulsar Timing Array – the Westerbork Synthesis Radio Telescope in the Netherlands, Germany’s Effelsberg Radio Telescope, the Lovell Telescope in the UK , France’s Nancay Radio Telescope and the Sardinia Radio Telescope in Italy.

Westerbork Synthesis Radio Telescope, an aperture synthesis interferometer near World War II Nazi detention and transit camp Westerbork, north of the village of Westerbork, Midden-Drenthe, in the northeastern Netherlands

MPIFR/Effelsberg Radio Telescope, in the Ahrgebirge (part of the Eifel) in Bad Münstereifel, Germany

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Lovell Telescope, Jodrell Bank

Nancay decametric radio telescope located in the small commune of Nançay, two hours’ drive south of Paris, France

Sardinia Radio Telescope based in Pranu Sanguni, near Sant’Andrea Frius and San Basilio, about 35 km north of Cagliari (Sardinia, Italy).

This multinational effort monitors 18 highly precise pulsars in the European sky to search out any timing anomalies, potential evidence of gravitational waves – fluctuations in the fabric of spacetime caused by powerful cosmic events.

For PulChron, these radio telescope measurements are used to steer the output of an active hydrogen maser atomic clock with equipment based in the Galileo Timing and Geodetic Validation Facility – combining its extreme short- and medium-term stability with the longer-term reliability of the pulsars. A ‘paper clock’ record is also generated out of the measurements, for subsequent post-processing checks.

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Atomic clocks at ESTEC

ESA established the Timing and Geodetic Validation Facility in the early days of the Galileo programme, first to prepare for ESA’s two GIOVE test satellites and then in support of the world-spanning Galileo system, based on ‘Galileo System Time’ which needs to remain accurate to a few billionths of a second. The Facility continues to serve as an independent yardstick of Galileo performance, linked to monitoring stations across the globe, as well as a tool for anomaly investigation.

Stefano adds: “The TGVF provided a perfect opportunity to host the PulChron because it is capable of integrating such new elements with little effort, and has a long tradition in time applications, having been used even to synchronise time and frequency offset of the Galileo satellites themselves.”

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PulChron setup

PulChron’s accuracy is being monitored down to a few billionths of a second using ESA’s adjacent UTC Laboratory, which harnesses three such atomic hydrogen maser clocks plus a trio of caesium clocks to produce a highly-stable timing signal, contributing to the setting of Coordinated Universal Time, UTC – the world’s time.

The gradual diversion of pulsar time from ESTEC’s UTC time can therefore be tracked – anticipated at a rate of around 200 trillionths of a second daily.

This project is supported through ESA’s Navigation Innovation and Support Programme (NAVISP), applying ESA’s hard-won expertise from Galileo and Europe’s EGNOS satellite augmentation system to new satellite navigation and – more widely – positioning, navigation and timing challenges.

PulChron is being led for ESA by GMV in the UK in collaboration with the University of Manchester and the UK’s NPL National Physical Laboratory.

See the full article here .


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The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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#astronomy, #astrophysics, #pulchron-system-measures-the-passing-of-time-using-millisecond-frequency-radio-pulses-from-multiple-fast-spinning-neutron-stars, #basic-research, #cosmology, #dame-susan-jocelyn-bell-burnell, #esa, #esa-sets-clock-by-distant-spinning-stars, #neutron-stars, #pulsar-timing-arrays-ptas

Netherlands Institute for Radio Astronomy: “Super-slow pulsar challenges theory”

ASTRON bloc

Netherlands Institute for Radio Astronomy

23/10/2018

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Artist’s conception of the newly discovered 23.5-second pulsar. Radio pulses originating from a source in the constellation Cassiopeia are seen travelling towards the core of the LOFAR telescope array. This source is a highly magnetised radio pulsar, shown in the inset image. The pulses and sky image are derived from the actual LOFAR data. Credit: Danielle Futselaar and ASTRON.

Women in STEM-Dame Susan Jocelyn Bell Burnell

Dame Susan Jocelyn Bell Burnell, discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

An international team of astronomers have discovered the slowest-spinning radio pulsar yet known. The neutron star spins around only once every 23.5 seconds and is a challenge for theory to explain. The researchers, including astronomers at the University of Manchester, ASTRON and the University of Amsterdam, carried out their observations with the LOFAR telescope, whose core is located in the Netherlands.

SKA LOFAR core (“superterp”) near Exloo, Netherlands

ASTRON LOFAR Radio Antenna Bank, Netherlands

Their findings will soon appear in the Astrophysical Journal.

Pulsars are rapidly rotating neutron stars that produce electromagnetic radiation in beams that emanate from their magnetic poles. These “cosmic lighthouses” are born when a massive star explodes in a supernova. Thereafter, a super-dense ball of material is left behind – rapidly spinning, and with a diameter of only about 20 kilometers. The fastest-spinning pulsar rotates once each 1.4 milliseconds. Until now, the slowest-spinning pulsar known had a period of 8.5 seconds. Now researchers have discovered a much slower, 23.5-second, pulsar, which is located in the constellation Cassiopeia.

“It is incredible to think that this pulsar spins more than 15.000 times more slowly than the fastest spinning pulsar known.” said Chia Min Tan a PhD Student at the University of Manchester who discovered the pulsar. “We hope that there are more to be found with LOFAR”.

The astronomers discovered this new pulsar during the LOFAR Tied-Array All-Sky Survey. This survey is searching for pulsars in the Northern sky. Each survey snapshot of the sky lasts for one hour. This is much longer compared to previous surveys, and gave the sensitivity needed to discover this surprising pulsar.

Not only did the astronomers ‘hear’ the regular ticks of the pulsar signal, they could also ‘see’ the pulsar in LOFAR’s imaging survey. Co-author Cees Bassa (ASTRON): “This pulsar spins so remarkably slowly that we could see it blinking on and off in our LOFAR radio images. With faster pulsars that’s not possible.”

The pulsar is approximately 14 million years old, but still has a strong magnetic field. Co-author Jason Hessels (ASTRON and University of Amsterdam): “This pulsar was completely unexpected. We’re still a bit shocked that a pulsar can spin so slowly and still create radio pulses. Apparently radio pulsars can be slower than we expected. This challenges and informs our theories for how pulsars shine.”

Moving forward, the astronomers are continuing their LOFAR survey for new pulsars. They are also planning to observe their new find with the XMM-Newton space telescope. This telescope is designed to detect X-rays. If the super-slow pulsar is detected as a source of X-rays, then this will give important insights into its history and origin.

See the full article here .

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LOFAR is a radio telescope composed of an international network of antenna stations and is designed to observe the universe at frequencies between 10 and 250 MHz. Operated by ASTRON, the network includes stations in the Netherlands, Germany, Sweden, the U.K., France, Poland and Ireland.
ASTRON-Westerbork Synthesis Radio Telescope
Westerbork Synthesis Radio Telescope (WSRT)

ASTRON was founded in 1949, as the Foundation for Radio radiation from the Sun and Milky Way (SRZM). Its original charge was to develop and operate radio telescopes, the first being systems using surplus wartime radar dishes. The organisation has grown from twenty employees in the early 1960’s to about 180 staff members today.

#astron, #astronomy, #astrophysics, #basic-research, #cosmology, #neutron-stars, #newly-discovered-23-5-second-pulsar, #source-is-a-highly-magnetised-radio-pulsar, #the-lofar-telescope-whose-core-is-located-in-the-netherlands

From Caltech: “A Better Way to Model Stellar Explosions”

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Caltech

03/01/2018

Whitney Clavin
(626) 395-1856
wclavin@caltech.edu

1
Artist’s concept of two neutron stars colliding. Credit: NSF/LIGO/Sonoma State University/A. Simonnet

Caltech scientists create new computer code for calculating neutron stars’ “equation of state”.

Neutron stars consist of the densest form of matter known: a neutron star the size of Los Angeles can weigh twice as much as our sun.

Neutron star http://factslegend.org/20-interesting-neutron-star-facts/

Astrophysicists don’t fully understand how matter behaves under these crushing densities, let alone what happens when two neutron stars smash into each other or when a massive star explodes, creating a neutron star.

One tool scientists use to model these powerful phenomena is the “equation of state.” Loosely, the equation of state describes how matter behaves under different densities and temperatures. The temperatures and densities that occur during these extreme events can vary greatly, and strange behaviors can emerge; for example, protons and neutrons can arrange themselves into complex shapes known as nuclear “pasta.”

But, until now, there were only about 20 equations of state readily available for simulations of astrophysical phenomena. Caltech postdoctoral scholar in theoretical astrophysics Andre da Silva Schneider decided to tackle this problem using computer codes. Over the past three years, he has been developing open-source software that allows astrophysicists to generate their own equations of state. In a new paper in the journal Physical Review C, he and his colleagues describe the code and demonstrate how it works by simulating supernovas of stars 15 and 40 times the mass of the sun.

The research has immediate applications for researchers studying neutron stars, including those analyzing data from the National Science Foundation’s Laser Interferometer Gravitational-wave Observatory, or LIGO, which made the first detection of ripples in space and time, known as gravitational waves, from a neutron star collision, in 2017. That event was also witnessed by a cadre of telescopes around the world, which captured light waves from the same event.

UC Santa Cruz

UC Santa Cruz

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A UC Santa Cruz special report

Tim Stephens

Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

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The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

“Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

THE MERGER

Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).


VIRGO Gravitational Wave interferometer, near Pisa, Italy

Caltech/MIT Advanced aLigo Hanford, WA, USA installation


Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

ESA/eLISA the future of gravitational wave research

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Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

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The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.


A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.

ALL THE GOLD IN THE UNIVERSE

It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

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The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

RIPPLES IN THE FABRIC OF SPACE-TIME

Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

“This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”

IN THIS REPORT

Neutron stars
A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

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Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

“We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

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David Coulter, graduate student

The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

“I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

“Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

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Charles Kilpatrick, postdoctoral scholar

Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

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Ariadna Murguia-Berthier, graduate student

“In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

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Matthew Siebert, graduate student

“It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

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César Rojas Bravo, graduate student

Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

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Yen-Chen Pan, postdoctoral scholar

“There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

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Enia Xhakaj, graduate student

IN THIS REPORT

Scientific Papers from the 1M2H Collaboration

Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger

PRESS RELEASES AND MEDIA COVERAGE


Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

Press releases:

UC Santa Cruz Press Release

UC Berkeley Press Release

Carnegie Institution of Science Press Release

LIGO Collaboration Press Release

National Science Foundation Press Release

Media coverage:

The Atlantic – The Slack Chat That Changed Astronomy

Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

Science – Merging neutron stars generate gravitational waves and a celestial light show

CBS News – Gravitational waves – and light – seen in neutron star collision

CBC News – Astronomers see source of gravitational waves for 1st time

San Jose Mercury News – A bright light seen across the universe, proving Einstein right

Popular Science – Gravitational waves just showed us something even cooler than black holes

Scientific American – Gravitational Wave Astronomers Hit Mother Lode

Nature – Colliding stars spark rush to solve cosmic mysteries

National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

Associated Press – Astronomers witness huge cosmic crash, find origins of gold

Science News – Neutron star collision showers the universe with a wealth of discoveries

UCSC press release
First observations of merging neutron stars mark a new era in astronomy

Credits

Writing: Tim Stephens
Video: Nick Gonzales
Photos: Carolyn Lagattuta
Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
Design and development: Rob Knight
Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

Dark Energy Survey


Dark Energy Camera [DECam], built at FNAL


NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

Noted in the vdeo but not in te article:

NASA/Chandra Telescope

NASA/SWIFT Telescope

NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

Prompt telescope CTIO Chile

NASA NuSTAR X-ray telescope

“The equations of state help astrophysicists study the outcome of neutron star mergers—they indicate whether a neutron star is ‘soft’ or ‘stiff,’ which in turn determines whether a more massive neutron star or a black hole forms out of the collision,” says da Silva Schneider. “The more observations we have from LIGO and other light-based telescopes, the more we can refine the equation of state—and update our software so that astrophysicists can generate new and more realistic equations for future studies.”

See the full article here

That event was also witnessed by a cadre of telescopes around the world, which captured light waves from the same event.

See the full article here .

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The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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From Science Magazine: “Gravitational waves help reveal the weight limit for neutron stars, the densest objects in the cosmos”

AAAS
Science Magazine

Feb. 15, 2018
Adrian Cho

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To derive the new mass limit, astrophysicists teased out the evolution of the famed merger of two neutron stars, spotted on 17 August 2017 and shown in this artist’s conception. University of Warwick/Mark Garlick/Wikimedia Commons (CC BY 4.0)

How heavy can neutron stars get? Astrophysicists have long wondered how massive these stellar corpses could be without collapsing under their own gravity to form a black hole. Last year’s blockbuster observations of two neutron stars merging revealed a collapse as it happened, enabling four different groups to converge on the maximum mass—about 2.2 times that of the sun.


“I’m encouraged that they all agree,” says James Lattimer, a nuclear astrophysicist at the State University of New York in Stony Brook. A solid mass limit for neutron stars will help theorists understand these mysterious objects. “Of all the characteristics of a neutron star, the two most important are the maximum mass and the radius,” Lattimer says.

A dying star can have one of three afterlives. A lightweight star shrinks into a white dwarf, an Earth-size sphere of carbon. A heavy star explodes when its massive core collapses to an infinitesimal point: a black hole. A star in the middle range—8 to 25 solar masses—also explodes, but leaves behind a fantastically dense sphere of nearly pure neutrons measuring a couple of dozen kilometers across: a neutron star.

As the neutron stars spiraled into each other, gravitational-wave detectors in the United States and Italy sensed ripples in space generated by the whirling bodies. The waves allowed physicists to peg their combined mass at 2.73 solar masses. Two seconds after the gravitational waves, orbiting telescopes detected a powerful, short gamma ray burst. Telescopes on Earth spotted the event’s afterglow, which faded over several days from bright blue to dimmer red.

Together, the clues suggest the merger first produced a spinning, overweight neutron star momentarily propped up by centrifugal force. The afterglow shows that the merger spewed between 0.1 and 0.2 solar masses of newly formed radioactive elements into space, more than could have escaped from a black hole. The ejected material’s initial blue tint shows that at first, it lacked heavy elements called lanthanides. A flux of particles called neutrinos presumably slowed those elements’ formation, and a neutron star radiates copious neutrinos. The short gamma ray burst, the supposed birth cry of a black hole, indicates that the merged neutron star collapsed in seconds.

To derive their mass limits, the teams dove into the details of the spinning neutron star. They generally argue that at first the outer layers of the merged neutron star likely spun faster than its center. Then it flung off material and slowed to form a rigid spinning body whose mass researchers could calculate from the masses of the original neutron stars minus the ejected material. The fact that this spinning neutron star survived only momentarily suggests that its mass was close to the limit for such a spinner.

That last inference is essential, Rezzolla says. Theory suggests that the mass of a rigidly spinning neutron star can exceed that of a stationary one by up to 18%, he says. That scaling allows researchers to infer the maximum mass of a stationary, stable neutron star. The whole argument works because the initial neutron stars weren’t so massive that they immediately produced a black hole or so light that they produced a spinning neutron star that lingered longer, Shibata says. “This was a very lucky event,” he says.

The analyses are persuasive, Lattimer says, although he quibbles with the precision implied in numbers such as 2.17 solar masses. “If you say 2.2 plus or minus a 10th, I would think it gets the same message across.”

See the full article here .

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