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The Neutron Star
Posted: Sun Aug 19, 2018 2:30 am
Alex Fleming, Graduate Research Assistant at Texas A&M University
How can a beam of light travel around the Earth roughly 7 times
in a second and a neutron star can supposedly rotate 1,000 times
in a second? Wouldn’t the rotational speed of the neutron star
exceed the speed of light?
Answered Fri · Upvoted by David Vanderschel, PhD Mathematics &
Physics, Rice (1970) and Paddy Alton, PhD in Astrophysics.
The reason we know that a neutron star CAN spin up to 716 times
in a second is because we have measured this in the fastest
spinning pulsar on record. A pulsar is a neutron star that has
a jet of high energy photons going off in two directions at
opposite poles. These photons are created along the direction
of the terrifyingly strong magnetic field generated by the neutron
star. The magnetic poles, just like on Earth, can occur on an axis
other than the axis of rotation. And as such, the pulsar acts kind
of similar to a lighthouse, sweeping a beam of light in a circle.
We can see a pulsar when we just happen to be in the direct path
of this beam of light. When we see this light, we can simply count
the number of pulses that we see in a second and we know how rapidly
the neutron star is rotating.
Now to answer your question. I've read a lot of the given answers
that simply say how large a neutron star is. The reason we know how
large the neutron star is actually is BECAUSE people first asked
the very question you asked. The speed of light is actually an upper
limit that theoretical nuclear astrophysicists used to take a first
guess at approximating the radius of a neutron star. We know THAT
a neutron star can rotate at 700 times a second. Since the speed of
light is the fastest anything can go, that means that a perfectly
spherical object with an equatorial tangential velocity of the
speed of light and spinning 700 times a second would have a radius
of about 40 miles. This is a crude estimate, but it does tell us
that we cannot have a radius larger than this.
We can also use the mass of the neutron star to set a lower limit
on this radius. Within some minimum radius, a neutron star of a
given mass will collapse into a black hole. Knowing the mass, and
how fast its spinning can give us a definite range. With the help
of LIGO and other gravitational wave detectors, we can hopefully
in the future get better ideas of the upper and lower limits of
the mass of neutron stars.
These two numbers, speed of rotation and mass, can help give us a
definite range of the size of a neutron star. To figure out the
EXACT radius of a given neutron star of a given mass is actually
a tremendous challenge, and still an ongoing problem in theoretical
nuclear astrophysics. We have to create models that use nuclear
physics and special and general relativity to take as inputs a set
of conditions we think exist inside neutron stars and then have
our model spit out a guess for the mass or radius. If the mass is
too large for too small a radius, it would collapse into a black
hole, the model is rejected. If the radius is so large that it
would break the cosmic speed limit, this too must be thrown out.
We have other conditions that limit the range further, but the
mass and rotational velocity are enough to make a good first guess.
So finally to answer your question, would the rotational speed of
a neutron star exceed the speed of light? No, because astrophysicists
based our best guess of the radius of a neutron star with the
speed of light in mind.
Re: The Neutron Star
Posted: Sun Oct 21, 2018 2:20 pm
PSR J1748-2446ad is the fastest-spinning pulsar known, at 716 Hz, or 716 times
per second. This pulsar was discovered by Jason W. T. Hessels of McGill University
on November 10, 2004 and confirmed on January 8, 2005. It has been calculated
that the neutron star contains slightly less than two times the mass of the Sun,
within the typical range of neutron stars. Its radius is constrained to be less
than 16 km. At its equator it is spinning at approximately 24% of the speed of
light, or over 70,000 km per second. The pulsar is located in a globular cluster
of stars called Terzan 5, located approximately 18,000 light-years from Earth in
the constellation Sagittarius.
The location of PSR J1748-2446ad in the night sky. The pulsar is located in the
center of the yellow square. It is too faint in this image to be visible against
It is part of a binary system and undergoes regular eclipses with an eclipse
magnitude of about 40%. Its orbit is highly circular with a 26-hour period.
The other object is about 0.14 solar masses, with a radius of 5–6 solar radii.
Hessels states that the companion may be a "bloated main-sequence star, possibly
still filling its Roche Lobe". Hessels goes on to speculate that gravitational
radiation from the pulsar might be detectable by LIGO.
Re: The Neutron Star
Posted: Tue Mar 26, 2019 11:10 pm
Asked by Jonathan Fox...
Neutron stars are created when a star around eight to ten
times the mass of our Sun runs out of fuel. The outward
pressure generated by fusion reduces rapidly, allowing
gravity to pull the star in on itself and trigger a
supernova, where the outer layers of a star’s atmosphere
get blown into space. The remaining matter continues to
collapse under gravity, forcing electrons and protons to
be squashed together and become neutrons. The neutron star
will have less mass than its parent star (typically about
1.4-times the mass of the Sun), but this mass will be
confined by gravity to a region of approximately
20 kilometers (12 miles) across, leading to an
incredibly dense object. It is this density (a
teaspoon full of neutron star would have a mass
of about a billion tons) that truly defines a
A neutron star, pictured here next to Manhattan,
New York, for scale, are highly dense objects.
Re: The Neutron Star
Posted: Sat Apr 06, 2019 7:28 am
Playing With Neutron Stars....
Nelson Cunnington, Enthusiast...wants to bring a cubic meter of
neutron star material to Earth.....
There are a number of challenges to this scenario that we can’t
solve with our technology....
A cubic meter of neutronium would mass around 4 × 1017 kg/m³.
So that would be 400 trillion tonnes, or about the mass of
an asteroid 45 km across.
The gravity in the center of each face would be around 11
million g, and at each corner 3.5 million g. One hundred
meters away, the gravity would be only 267 g, and at a
kilometer 2.7 g. At 10 km, you would probably not notice
the change in your local vertical. So the first thing
that would happen is that everything around the cube would
be drawn to it, very quickly. At a hundred metres the fall
would take a fraction of second; at 1650m stuff would start
rolling towards it as though down a 45° slope at 1.4 g.
When the matter hit the surface (traveling at about a
kilometer a second or less) it would be compressed by the
extreme gravity into a form known as condensed matter,
where the nucleons are in contact and the electrons freely
travel among them. This is very dense itself, about a million
tonnes per cubic meter. A hemisphere of granite a kilometer in
radius would be about 750,000 tonnes, so your cube would acquire
a surface of condensed matter less than half-a-meter thick.
There would be a great deal of energy released as this happened,
equivalent to a hundred kiloton-scale nuclear weapon, but spread
out over several seconds.
Presumably, you are holding up the mass with tractor beams. If
you released the tractor beams as you realized what an utter
mistake you had made bringing this mass to Earth, it would fall
toward the Earth at one gee. Hitting the surface, it wouldn’t
pause, being so much denser than the rock on which you built your
high-density physics laboratory that it would slip through it like
a steel weight through high-altitude air. Presumably there would
be a terminal velocity for neutronium through rock, which would
lessen as the cube got deeper, but my math isn’t up to working
it out. Assuming it didn’t slow down, in about twenty-one minutes
it would have fallen to the center of the Earth, and then begun
to climb again so that it would appear at the antipode from the
site of your former laboratory twenty-one minutes later. By this
time it should have accumulated quite a thickness of condensed
and normal matter, though, so it wouldn’t necessarily get to the
surface again, instead oscillating back and forth at a decaying
rate until it slowed enough to settle at the center. Before that,
though, as it falls through the surface of the Earth, the tidal
forces of the extreme mass passing will trigger a local earthquake,
quite likely at the high end of the magnitude scale, which will
level buildings for kilometers around.
But perhaps as well as the tractor beams you accidentally switch
off the force-field that contains the neutronium cube? As others
have mentioned, stupendous though it is, the mass of a one-meter
cube isn’t enough to keep the neutronium in a stable state, and
it will start to disintegrate immediately. The half-life of a
free neutron is about ten minutes, leading to it decaying into
a proton, an electron and a neutrino. These particles are stable,
but the sheer quantity of the first conversions will lead to a
gigantic explosion, turning the cube and everything around it
into plasma. An explosion that would make our most powerful
nuclear weapons look like firecrackers.
Better to perform this kind of experiment OFF the Earth!
Re: The Neutron Star
Posted: Mon Apr 08, 2019 2:22 am
In the aftermath of a 8 – 20 solar mass star’s demise, we find a weird
little object known as a neutron star. Neutrons stars are incredibly
dense, spin rapidly, and have very strong magnetic fields. Some of
them we see as pulsars, flashing in brightness as they spin.
Neutrons stars with the strongest magnetic fields are called
magnetars, and are capable of colossal bursts of energy that
can be detected over vast distances.
Re: The Neutron Star
Posted: Sun Apr 28, 2019 5:48 pm
Making More Gold (& Silver)!
By Discover Staff | April 25, 2019 6:15 pm...
For just the second time, physicists working on the Laser Interferometer
Gravitational-Wave Observatory (LIGO) have caught the gravitational waves
of two neutron stars colliding to likely form a black hole. The ripples
in space - time traveled some 500 million light-years and reached the
detectors at LIGO, as well as its Italian sister observatory, Virgo, at
around 4 a.m. E.T. on Thursday, April 25. Team members say there’s a more
than 99 percent chance that the gravitational waves were created from a
binary neutron star merger.
In the moments after the event, a notice went out alerting astronomers
around the world to turn their telescopes to the heavens in hopes of
catching light from the explosion, called a kilonova. Kilonovas are
1,000 times brighter than normal novas, and they create huge amounts
of heavy elements, like gold and platinum. That brightness makes it
easy for astronomers to find these events in the night sky — provided
they’ve been given a heads-up and location from LIGO first. LIGO’s
twin L-shaped observatories — one in Washington state and one in
Louisiana — work by shooting a laser beam down the long legs of their
“L.” Their experimental setup is precise enough that even the minimal
disturbance caused by a passing gravitational wave is enough to trigger
a slight change in the laser’s appearance. It made the first ever
detection of gravitational waves in 2016. Then it followed up by
detecting merging neutron stars in 2017. Scientists use any slight
delays between when signals reach the detectors to help them better
triangulate where the waves originated in the sky. But one of LIGO’s
twin detectors was offline Thursday when the gravitational wave reached
Earth, making it hard for astronomers to triangulate exactly where the
signal was coming from. That sent astronomers racing to image as many
galaxies as they could across a region covering one-quarter of the sky.
And instead of finding one potential binary neutron star merger,
astronomers turned up at least two different candidates. Now the
question is which, if any, are related to the gravitational wave
that LIGO saw. Sorting that out will require more observations, which
were already happening around the world as darkness fell. “I would assume
that every observatory in the world is observing this now,” says astronomer
Josh Simon of the Carnegie Observatories. “These two candidates (they’ve)
found are relatively close to the equator, so they can be seen from both
the Northern and Southern Hemisphere.” Simon also says that, as of Thursday
afternoon in the United States, telescopes in Europe and elsewhere should
be gathering spectra on these objects. His fellow astronomers at the
Carnegie Observatories turned their telescopes at Chile’s Las Campanas
Observatory to the event Thursday night.
LIGO’s first detection of a neutron star merger came in August of 2017,
when scientists detected gravitational ripples from a collision that
occurred about 130 million light years away. Astronomers around the
world immediately turned their telescopes to the collision’s location
in the sky, allowing them to gather a range of observations from across
the electromagnetic spectrum. The 2017 detection was the first time an
astronomical event had been observed with both light and gravitational
waves, ushering in a new era of “multi-messenger astronomy.” The resulting
information gave scientists invaluable data on how heavy elements are
created, a direct measurement of the expansion of the universe and
evidence that gravitational waves travel at the speed of light, among
other things. This second observation appears to have been slightly too
far away for astronomers to get some of of the data they had hoped for,
such as how nuclear matter behaves during the intense explosions.
And astronomers still aren’t sure whether the first detection they made
came from a typical neutron star merger or whether it was more exotic.
But to figure that out, they’d need observations as early as possible,
and precious hours have already passed. “After the first event, it was
clear that a lot of the action was going on immediately after the explosion,
so we wanted to get observations as soon as possible,” Simon says. In
this case, with one of LIGO’s detectors down, they couldn’t find the
object as quickly as they did in 2017. So far, one difference is that,
unlike last time, astronomers haven’t spotted any signs of gamma - ray
bursts, says University of Wisconsin-Milwaukee physicist Jolien Creighton,
a LIGO team member.
But regardless, having additional observations should help us learn more
about these extreme cosmic collisions. “It gives us a much better handle
on the rate of such collisions,” says Stefan Ballmer, associate physics
professor at Syracuse University and LIGO member. “The upshot: if we just
observe a little longer we will get the strong signal we are hoping for.”
LIGO just started its third observing run a few weeks ago. And, in the past,
these detections were kept a closely guarded secret until they were confirmed,
peer-reviewed and published. But with this latest round, LIGO and Virgo
have opened their detections up to the public. In this latest run, LIGO
has also already detected three potential black hole collisions, bringing
its total lifetime haul to 13.
Re: The Neutron Star
Posted: Sun Apr 28, 2019 8:44 pm
....one cubic meter of matter from a neutron star were moved to Earth?
It would weigh 850 billion tons. Round that to a trillion tons, and it
weighs the same as this ball of ice:
As it approached Earth, it would accelerate, hit the atmosphere and not
slow down. It would punch a hole in the ground and be pulled to the
center of the Earth as fast as if there was no liquid rock to fall through.
It would slow as it fell due to reduced gravity pull nearer the center,
not accelerate. It would then oscillate through the center until it stops.
Re: The Neutron Star
Posted: Fri May 03, 2019 1:47 am
Last Dance Of Neutron Star
The Hanford LIGO observatory near Richland (WA) may have again
made scientific history in its first month of a new observing run.
Along with two other collaborating gravitational wave observatories,
it possibly detected the gravitational waves created as a black
hole swallowed a neutron star about 1.2 billion light years from
Earth. A neutron star is the smallest, densest type of star known
to exist. A teaspoon-sized chunk of a neutron star weighs a billion
https://www.thenewstribune.com/news/sta ... rylink=cpy
Re: The Neutron Star
Posted: Fri May 03, 2019 2:41 pm
Here is something interesting about a neutron star falling in to a black hole.
The gravitational force on the near side of an object exceeds that of the far side of an object, because gravity decreases with distance. this is called the TIDAL FORCE. For people on the surface of Earth, the tidal forces between head and feet are negligible. However, Earth exerts significant tidal forces on the Moon, despite the Moon being further away, due to the Moon's size.
Before we begin, let us calculate the force (in solar mass miles per second squared) exerted by a 1.5 solar mass, 12-mile radius neutron star upon a 0.001 solar mass "slice" on the surface. In cubic miles per solar mass per second squared, the GRAVITATIONAL CONSTANT is 3.18479 E 10.
The gravitational force of a neutron star upon its surface is 3.18749 E 10*1.5*0.001/12^2=33,030.2083 solar mass miles per second squared.
What happens if the neutron star's near side if forty-five miles from the center of a black hole with eight solar masses?
The black hole's pull on a 0.001 solar mass slice on the near side is 3.18749 E 10*8*0.001/45^2=125,925.5309 solar mass miles per second squared.
The far side is twenty-four miles from the near side, so the force exerted on the far side is 3.18749 E 10*8*0.001/69^2=53,560.0084 solar mass miles per second squared.
The tidal force is the difference. 125,925.5309-53560.0084= 72,365.5225 solar mass miles per second squared.
The tidal force exceeds the gravitational force of the neutron star itself, so the neutron star had already been torn apart.
An interesting thing happens. Neutron stars have this tremendous outbound pressure, called NEUTRON DEGENERACY PRESSURE. Only gravity from the neutron star's high mass and small size keeps the thing together. If a 1.5 solar mass neutron star is torn apart by tidal forces, then the pieces will not have enough mass to counteract the neutron degeneracy pressure, and they will explode. Some of the material will fall into the black hole, and some will escape to infinity. It is possible that the explosion of a neutron star fragment could create heavy elements, like the neutron star collision did.
For a 1.5 solar mass neutron star falling into an 8 solar mass black hole, when do tidal forces tear the neutron star apart? It has to be when the tidal force equals the neutron star's gravity. Using n as the near distance, we must solve these equations for n. 3.18749 E 10*8*0.001/n^2-3.18749E10*8*0.001/(n+24)^2=254,999,200/n^2-254,999,200/(n+24)^2=254,999,200(1/n^2-1/(n+24)^2=33,030.2083 solar mass miles per second squared. 1/n^2-1/(n+24)^2=1/n^2-1/(n^2+48n+576)=0.000129531 per mile squared per second squared. 1-n^2/(n^2+48n+576)=0.000129531n^2
0.000129531n^4+0.006217488n^3+0.074609856n^2-48n-576=0. We only need to solve the quadratic. We get n=61.59325 miles (61 mi, 1044 yd, just under 100 km) So it is around sixty miles from an 8 solar mass black hole that a 1.5 solar mass neutron star with a 12-mile radius would start to break apart before its pieces explode.
But what about a supermassive black hole? Let us take the example of a 4 million solar mass black hole. The radius is
2*3.18749 E 10*4000000/186282^2=7,348,471.833 miles. The tidal forces across this same neutron star, at the event horizon, are 3.18749 E 10*4000000*0.001/7,348,471.833^2-3.18749 E *4000000*0.001/(7,348,471.833+24)^2=1.54226E-5 solar mass miles per second squared. This is much less than the force between the neutron star and a 0.001 solar mass sliver at the surface. So the neutron star will enter the black hole in one piece. It will eventually be torn apart as it plunges towards the center, but no one outside the hole will observe it.
Re: The Neutron Star
Posted: Tue May 07, 2019 3:04 pm
Original Gold-Digger Found!
Two neutron stars rip each other apart to form a black hole in this
NASA simulation. New research suggests that a stellar collision like
this occurred very close to our solar system some 4.6 billion years
ago, showering our cosmic neighborhood with many of the heavy elements
crucial to life.
https://www.livescience.com/65411-neutr ... 0190506-ls