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What Is A Neutron Star?


Neutron stars are created when giant stars die in supernovae and their cores collapse, with the protons and electrons essentially melting into each other to form neutrons. Neutron stars are city-size stellar objects with a mass about 1.4 times that of the sun. Born from the explosive death of another, larger stars, these tiny objects pack quite a punch.

When stars three times as massive as the sun explodes in a violent supernova, their outer layers can blow off in an often-spectacular display, leaving behind a small, dense core that continues to collapse. Gravity presses the material in on itself so tightly that protons and electrons combine to make neutrons, yielding the name "neutron star." This is how it is named neutron star.



Ordinary stars maintain their spherical shape because they have the gravity of their gigantic mass tries to pull their gas toward a central point, but it is balanced by the energy from nuclear fusion in their cores, which exerts an outward pressure. At the end of their lives, when stars are burned through their available fuel, their internal fusion reactions cease. The stars' outer layers rapidly collapse inward, bouncing off the thick core and then blasting out again as a violent supernova.

After the star went supernova the dense core continues to collapse, generating pressures so high that protons and electrons are squeezed together into neutrons, as well as lightweight particles called neutrinos that escape into the distant universe. The end result is a star whose mass is 90% neutrons, which can't be squeezed any tighter, and therefore the neutron star can't break down any further.



Neutron stars pack their mass inside a 20-kilometre (12.4 miles) diameter. They are so dense that a single teaspoon would weigh a billion tons — assuming you somehow managed to snag a sample without being captured by the body's strong gravitational pull. On average, gravity on a neutron star is 2 billion times stronger than gravity on Earth. In fact, it's strong enough to significantly bend radiation from the star in a process known as gravitational lensing, allowing astronomers to see some of the backsides of the star.

The power from the supernova that birthed it gives the star an extremely quick rotation, causing it to spin several times in a second. Neutron stars can spin as fast as 43,000 times per minute, gradually slowing over time.



The properties of neutron stars are utterly out of this world — a single teaspoon of neutron-star material would weigh a billion tons. If you were to somehow stand on their surface without dying, you'd experience a force of gravity 2 billion times stronger than what you feel on Earth.

An ordinary neutron star's magnetic field might be trillions of times stronger than Earth's. But some neutron stars have even more extreme magnetic fields, a thousand or more times the average neutron star. This creates an object known as a magnetar.  



Starquakes on the surface of a magnetar — the equivalent of crustal movements on Earth that generate earthquakes — can release tremendous amounts of energy. In one-tenth of a second, a magnetar might produce more energy than the sun has emitted in the last 100,000 years.

Astronomers first theorized about the existence of these bizarre stellar entities in the 1930s, shortly after the neutron was discovered. But it wasn't until 1967 that scientists had good evidence for neutron stars in reality. A graduate student named Jocelyn Bell at the University of Cambridge in England noticed strange pulses in her radio telescope, arriving so regularly that at first, she thought they might be a signal from an alien civilization, according to the American Physical Society. The patterns turned out not to be E.T. but rather radiation emitted by rapidly spinning neutron stars.



If a neutron star is part of a binary system that survived the deadly blast from its supernova (or if it captured a passing companion), things can get even more interesting. If the second star is less massive than the sun, it pulls mass from its companion into a Roche lobe, a balloon-like cloud of material that orbits the neutron star. Companion stars up to 10 times the sun's mass create similar mass transfers that are more unstable and don't last as long.

Stars more than 10 times as massive as the sun transfer material in the form of a stellar wind. The material flows along the magnetic poles of the neutron star, creating X-ray pulsations as it is heated.



By 2010, approximately 1,800 pulsars had been identified through radio detection, with another 70 found by gamma-rays. Some pulsars even have planets orbiting them — and some may turn into planets.

Types of neutron stars
Radio pulsars
Recycled pulsars
Millisecond pulsars
Magnetar
Soft gamma-ray repeater
Anomalous X-ray pulsar
Low-mass X-ray binaries (LMXB)
Intermediate-mass X-ray binaries (IMXB)
High-mass X-ray binaries (HMXB)
Accretion powered pulsar

Pulsars
Some neutron stars have jets of materials streaming out of them at nearly the speed of light. As these beams pan past Earth, they flash like the bulb of a lighthouse. Scientists called them pulsars after their pulsing appearance. Normal pulsars spin between 0.1 and 60 times per second, while millisecond pulsars can result in as much as 700 times per second.

When X-ray pulsars capture the material flowing from more massive companions, that material interacts with the magnetic field to produce high-powered beams that can be seen in the radio, optical, X-ray or gamma-ray spectrum. Because their main power source comes from the material from their companion, they are often called "accretion-powered pulsars." "Spin-powered pulsars" are driven by the star’s rotation, as high-energy electrons interact with the pulsar's magnetic field above their poles. Young neutron stars before they cool can also produce pulses of X-rays when some parts are hotter than others.



As material within a pulsar accelerates within the magnetosphere of a pulsar, the neutron star produces gamma-ray emission. The transfer of energy in these gamma-ray pulsars slows the spin of the star.

The supernova that gives rise to a neutron star imparts a great deal of energy to the compact object, causing it to rotate on its axis between 0.1 and 60 times per second, and up to 700 times per second. The formidable magnetic fields of these entities produce high-powered columns of radiation, which can sweep past the Earth-like lighthouse beams, creating what's known as a pulsar.



The flickering of pulsars is so predictable that researchers are considering using them for spaceflight navigation.

"Some of these millisecond pulsars are extremely regular, clock-like regular," Keith Gendreau of NASA's Goddard Space Flight Center in Maryland, told members of the press in 2018.

"We use these pulsars the same way we use the atomic clocks in a GPS navigation system," Gendreau said.

Magnetars

The average neutron star boasts a powerful magnetic field. Earth's magnetic field is around 1 gauss, and the sun's magnetic field is around a few hundred gauss, according to astrophysicist Paul Sutter. But a neutron star has a trillion-gauss magnetic field.



Magnetars have magnetic fields a thousand times stronger than the average neutron star. The resulting drag causes the star to take longer to rotate. 

"That puts magnetars in the No. 1 spot, reigning champions in the universal 'strongest magnetic field' competition," Sutter said. "The numbers are there, but it's hard to wrap our brains around them."



These fields wreak havoc on their local environments, with atoms stretching into pencil-thin rods near magnetars. The dense stars can also drive bursts of high-intensity radiation.

Get too close to one (say, within 1,000 kilometres, or about 600 miles), and the magnetic fields are strong enough to upset not just your bioelectricity (rendering your nerve impulses hilariously useless) but your very molecular structure. In a magnetar's field, you just kind of dissolve."

Collision Of Neutron Star

Like normal stars, two neutron stars can orbit one another. If they are close enough, they can even spiral inwards to their doom in an intense phenomenon known as a "kilonova."

The collision of two neutron stars made waves heard 'round the world in 2017 when researchers detected gravitational waves and light coming from the same cosmic smashup. The research also provided the first solid evidence that neutron-star collisions are the source of much of the universe's gold, platinum and other heavy elements.



"The origin of the really heaviest chemical elements in the universe has baffled the scientific community for quite a long time," Hans-Thomas Janka, a senior scientist at MPA, said in a statement. "Now, we have the first observational proof for neutron star mergers as sources; in fact, they could well be the main source of the r-process elements," which are elements heavier than iron, like gold and platinum.

The powerful collision released enormous amounts of light and created gravitational waves that rippled through the universe. But what happened to the two objects after their smashup remains a mystery.

"We don't actually know what happened to the objects at the end," David Shoemaker, a senior research scientist at MIT and a spokesman for the LIGO Scientific Collaboration, said at a 2017 news conference. "We don't know whether it's a black hole, a neutron star or something else." The observations are thought to be the first of many to come.



"We expect that more neutron-star mergers will soon be observed and that the observational data from these events will reveal more about the internal structure of matter," study lead author Andreas Bauswein, from the Heidelberg Institute for Theoretical Studies in Germany, said in a statement.

Can Neutron Star Become Blackhole?

When a star dies, it spent all of its energy and then collapses. Their difference lies in their parent star. When a dying star has a mass which is 1.4 to 3 times that of the sun, it will form a neutron star. Stars with a mass greater than 3 times the sun's mass, a black hole is formed. The maximum mass of a neutron star is 3 solar masses. If it gets more massive than that, then it will collapse into a quark star, and then into a black hole.



Some Interesting  Fact
1. In just the first few seconds after a star begins its transformation into a neutron star, the energy leaving in neutrinos is equal to the total amount of light emitted by all of the stars in the observable universe.

2. It’s been speculated that if there were life on neutron stars, it would be two-dimensional.

3. The fastest known spinning neutron star rotates about 700 times each second.

4. The wrong kind of neutron star could wreak havoc on Earth.

5. Despite the extremes of neutron stars, researchers still have ways to study them.

Researchers have considered using the stable, clock-like pulses of neutron stars to aid in spacecraft navigation, much like GPS beams help guide people on Earth. An experiment on the International Space Station called Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) was able to use the signal from pulsars to calculate the ISS’s location to within 10 miles (16 km). 



But a great deal remains to be understood about neutron stars. For instance, in 2019, astronomers spotted the most massive neutron star ever seen — with about 2.14 times the mass of our sun packed into a sphere most likely around 12.4 miles (20 km) across. At this size, the object is just at the limit where it should have collapsed into a black hole, so researchers are examining it closely to better understand the odd physics potentially at work holding it up. 



Accretion Of A Giant Planet Onto A White Dwarf Star


The Neptune-sized planet, which orbits an Earth-sized star, is being slowly evaporated by the white dwarf, causing the planet to lose some 260 million tons of material every day.

For the first time, astronomers have discovered evidence for a giant planet orbiting a tiny, dead white dwarf star. And, surprisingly, the Neptune-sized planet is more than four times the diameter of the Earth-sized star it orbits.



"This star has a planet that we can't see directly. But because the star is so hot, it is evaporating the planet, and we detect the atmosphere it is losing. In fact, the searing star is sending a stream of vaporized material away from the planet at a rate of some 260 million tons per day." Boris Gänsicke from the University of Warwick said in a press release.

The new discovery serves as the first evidence of a gargantuan planet surviving a star's transition to a white dwarf. It suggests that evaporating planets around dead stars may be somewhat common throughout the universe. And because our Sun, like most stars, will also eventually evolve into a white dwarf, the finding could even shed light on the fate of our solar system.



The white dwarf in question, dubbed WDJ0914+1914, sits about 1,500 light-years away in the constellation Cancer. Although the white dwarf is no longer undergoing nuclear fusion like a normal star, its lingering heat means it's still a blistering 49,500 degrees Fahrenheit (25,000 Celsius). That’s some five times hotter than the Sun.

Researchers initially flagged the smouldering stellar core for follow-up after sifting through about 7,000 white dwarfs identified by the Sloan Digital Sky Survey. When the team analyzed the unique spectra of WDJ0914+1914, they detected the chemical fingerprints of hydrogen, which is somewhat unusual. But they also picked out signs of oxygen and sulfur — elements they had never seen in a white dwarf before.



In order to get a better grasp of what was happening in the strange system, the team of researchers used the X-shooter instrument on the ESO's Very Large Telescope in Chile to carry out follow-up observations. Based on the more detailed look, the researchers learned that the unusual elements they thought were embedded in the white dwarf were actually coming from a disk of gas churning around the dead star.

"At first, we thought that this was a binary star with an accretion disk formed from mass flowing between the two stars. However, our observations show that it is a single white dwarf with a disk around it roughly 10 times the size of our Sun, made solely of hydrogen, oxygen and sulfur. Such a system has never been seen before, and it was immediately clear to me that this was a unique star." said Gänsicke.



After realizing just how unusual the white dwarf really was, the team shifted their focus to figuring out what the heck could create such a system.

"It took a few weeks of very hard thinking to figure out that the only way to make such a disk is the evaporation of a giant planet," said Matthias Schreiber, an astronomer at the University of Valparaiso in Chile, who was vital to determining the past and future evolution of the bizarre system. Their detailed analysis of the disk's composition matched what astronomers would expect if the guts of an ice giant like Uranus and Neptune were vaporized into space.



Based on Schreiber's calculations, the white dwarf's extreme temperature means it's bombarding the nearby giant planet — which is located 0.07 astronomical unit (AU) from the star, where 1 AU is the Earth-Sun distance — with high-energy photons. This is causing the planet to lose its mass at a rate of more than 3,000 tons per second.

But according to the paper, published Wednesday in Nature, "As the white dwarf continues to cool, the mass-loss rate will gradually decrease, and become undetectable in about 350 million years. And by then, the paper adds, the giant planet only will have lost "an insignificant fraction of its total mass," or about 0.04 Neptune masses.



Because the giant planet is located so close to the white dwarf, the researchers say it should have been destroyed during the stars' red giant phase. That is unless it migrated inward after the star transitioned to a white dwarf. 

"This discovery is major progress because over the past two decades we had growing evidence that planetary systems survive into the white dwarf stage," said Gänsicke. "We've seen a lot of asteroids, comets, and other small planetary objects hitting white dwarfs, and explaining these events requires larger, planet-mass bodies farther out. Having evidence for an actual planet that itself was scattered in is an important step."



The ultimate fate of our solar system. In 5 billion years, when the Sun burns through the last of the hydrogen in its core, it will move on to fusing concentric shells of hydrogen around its now-inert core. This unstable process will cause the Sun to balloon into a red giant, meaning it will swallow Mercury, Venus, and likely Earth.

But as the Sun expands, its gravitational grasp on its outer envelope of material gets more and more tenuous. Eventually, it will shed its outer layers into space. And once it does that, an alien astronomer would see a beautiful planetary nebula surrounding the Sun's burnt-out, incredibly hot core — known as a white dwarf.



In a companion paper also published Wednesday in Astrophysical Journal Letters, Schreiber and Gänsicke explore this scenario, detailing how the future white-dwarf Sun should, like WDJ0914+1914, evaporate our solar system's giant planets.



What If We had Two Suns in The Solar System?


For a long time, this was a purely theoretical question. Over the past decade or so, however, astronomers have found more than a dozen confirmed instances of “circumbinary planets”—that is, planets that orbit around a close double star.

A particularly interesting case is the planet Kepler-1647b, which circles two roughly sunlike stars. This planet also resides in the “habitable zone,” the region around the two stars where the planet could have the right temperature for liquid water.



What if Earth had two suns instead of one? Let’s consider a simple scenario. Suppose we replaced the sun with two closely matched stars, each half as bright as the Sun. In that case, the amount of energy reaching the Earth would still be the same, and life would still be possible here. Such equal-mass binaries are not uncommon, so this scenario seems perfectly plausible.

The mass of each of our new suns would be about 85% of the mass of our current sun. That may seem surprising, but the luminosity of a star is extremely sensitive to mass. Roughly speaking, luminosity goes as the 4th power of mass, so doubling the mass of a star increases its brightness by a factor of 16. A 15% mass reduction is enough to cut a star’s brightness in half.



The combined mass of Sun 1 and Sun 2 would be 1.7 times the mass of our current sun. Since their total gravity would be stronger, the length of a year would be a bit less: about 280 days instead of 365 days. Not that radical of a change, really.

So far so good. But would the Earth be stable in its new configuration, orbiting around two stars instead of one? The case of Kepler-1647b and other circumbinary stars gives a strong YES answer here. As long as the distance to the planet is at least about 4 times as great as the separation between the two stars, the planet just happily orbits around the stars’ centre of mass. If Sun 1 and Sun 2 are less than 15 million kilometres apart, then all of the planets in the solar system (even Mercury) could potentially be stable.



Just to be safe, let’s put the stars closer together, about 5 million kilometres apart. That’s not so different than the two stars of Kepler-1647, which are about 7 million miles apart. Our Sun 1 and Sun 2 would orbit each other once every 10 days or so. They would also each rotate with a 10-day period, which would make them a little more active than our current sun, but not outrageously so. The Kepler-1647 stars are reasonably peaceful.

The two suns would probably appear to orbit each other roughly edge-on as seen from Earth, which would lead to a strange new phenomenon: an eclipse of the sun by another sun! Because of the 10-day orbit, Sun 1 and Sun 2 would pass in front of each other every 5 days. The eclipses would last about 6 hours, and at peak would reduce the amount of energy reaching the Earth by about 30%–40%, depending on the exact geometry.



Eclipse days would be chilly, but the periods of reduced sunshine would be brief enough to average out smoothly into Earth’s overall climate. The double suns wouldn’t even look all that strange in the sky. At maximum separation, Sun 1 and Sun 2 would be only 2 degrees apart in the sky, just enough to give shadows a double edge. For about a half-day on either side of an eclipse, they'd seem to merge, though if they slipped behind a cloud you'd see an odd, oval shape from the overlapping disks. Sunsets would be pretty, a little different each night.

All the evidence so far, then, is that a planet like Tatooine in Star Wars really could exist, and Earth would do just fine if it were orbiting a double star instead of our one lonely sun. There’s really just one huge unsettled question: Could such a planet form in the first place?



Kepler-1647b is a giant gas planet, nearly twice the mass of Jupiter. Even the smallest known circumbinary planet, called Kepler-453b, is a heavyweight, bigger than Neptune.

It may be that the environment around a double star is too chaotic to create small, rocky planets like Earth. Then again, it’s also possible that other Earths with two suns are common, and our telescopes simply are not sensitive enough to find them. At least, not yet.



Fortunately, better instruments are coming soon. In the coming decade, the PLATO space telescope and huge new ground-based observatories like the Giant Magellan Telescope and the Extremely Large Telescope will tell us a lot more about all kinds of planets around other stars—including possible Earthlike planets with double suns lighting up their skies.



Black Holes Are Strange Sure But White Holes Are Mind-Blowing


White holes are black ones in reverse, spewing out matter– and they could give us our first glimpse of the quantum source of space-time.

In the textbooks, Gravitation and Cosmology, Nobel prizewinning physicist Steven Weinberg wrote that the existence of black holes “very hypothetical”, there is no [black hole] in the gravitational field of any known object of the universe”. He was dead wrong. Radio astronomers had already been detecting signals from matter falling into black holes for decades without realising. Today we have lots of evidence that the sky is teeming with them.




The story may now be repeating itself with white holes, which are essentially black holes in reverse. In another renowned textbook, the world-leading relativity theorist Bob Wald wrote that “there is no reason to believe that any region of the universe corresponds to” a white hole – and this is still the dominant opinion today. But several research groups around the world have recently begun to investigate the possibility that quantum mechanics could open a channel for these white holes to form. The sky might be teeming with white holes, too.

The reason to suspect white holes exist is that they could solve an open mystery: what goes on at the centre of a black hole. We see great amounts of matter spiralling around black holes and then falling in. All this falling matter crosses the surface of the hole, the “horizon” or point of no return, plummets towards the centre, and then? Nobody knows.




White holes are completely theoretical mathematical concepts. In fact, if you do black hole mathematics for a living, I'm told, ignoring the mass of the singularity makes your life so much easier.

They are not things that actually proven to exist. It's not like astronomers detected an unusual outburst of radiation and then developed hypothetical white hole models to explain them.




if white holes did exist, they would behave like reverse black holes – just like the math predicts. Instead of pulling material inward, a white hole would blast material out into space like some kind of white chocolate fountain.

White Holes only theoretically exist as long as there isn't a single speck of matter within the event horizon. As soon as a single atom of hydrogen drifted into the region, the whole thing would collapse. Even if white holes were created back at the beginning of the universe, they would have collapsed long ago, since our universe is already filled with stray matter.




In theory, a black hole singularity would compress down until the smallest possible size predicted by physics. Then it would rebound as a white hole. But because of the severe time dilation effect around a black hole, this event would take billions of years for even the lowest mass ones to finally get around to popping.

If there were microscopic black holes created after the Big Bang, they might get around to decaying and exploding as white holes any day now. Except, according to Stephen Hawking, they would have already evaporated.




Another interesting idea put forth by physicists is that a white hole might explain the Big Bang since this is another situation where a tremendous amount of matter and energy spontaneously appeared.

White Hole exists or not is still a mystery but it's a very fascinating topic. The more we study and understand our universe, the more our brain gets blown away.



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