Tag Archives: pulsars

ESO / L. Calçada

Neutron Stars Make Ant Hills Out of Mountains

The surfaces of neutron stars may feature mountains, albeit ones that are no more than millimetres tall, new research has revealed. The minuscule scale of neutron star mountains is a result of the intense gravity produced by these stellar remnants that are the second densest objects in the Universe after black holes.

Because neutron stars have the mass equivalent to a star like the Sun compressed into a diameter that is about the size of a city on Earth–about 10km– they have a gravitational pull at their surface that is as much as 40,000 billion times stronger than Earth’s.

This presses features on that surface flat, making for almost perfect spheres. Yet the new research, presented at the National Astronomy Meeting 2021 shows that these stellar remnants do feature some tiny topological deformations, analogous to mountains on a planet’s surface.

ESO / L. Calçada
Artist’s rendition of a neutron star. New research suggests mountains on such stellar remnants could be no more than a fraction of a millimetre tall. ESO / L. Calçada

The finding was a result of complex computer modelling by a team of researchers led by the University of Southhampton’s Fabian Gittins. The Ph.D. student’s team simulated a realistic neutron star and then calculated the forces acting upon it. What the research really shows is how well neutron stars can support deviations from a perfect sphere without its crust being strained beyond breaking point.

This revealed how mountains could be created on such dense stellar remnants and demonstrated that such formations would be no taller than a fraction of a millimetre.

“For the past two decades, there has been much interest in understanding how large these mountains can be before the crust of the neutron star breaks, and the mountain can no longer be supported,” says Gittins. These results show how neutron stars truly are remarkably spherical objects. “Additionally, they suggest that observing gravitational waves from rotating neutron stars maybe even more challenging than previously thought”.”

Mountain formation has been formulated for neutron stars before, but these new findings suggest such features would be hundreds of times smaller than the mountains of a few centimetres previously predicted. This is because those older models took the crusts of neutron stars to the edge of breaking point at every single point; something the up-to-date research suggests is less than realistic.

Neutron stars form when massive stars run out of fuel to power nuclear fusion. This means that the toward force balancing against gravity’s inward pull is cancelled and leads to the gravitational collapse of the star. During the course of this collapse, the massive star ejects its outer material in supernova explosions and leaving behind a core of ultradense material. This stellar remnant is only protected from further collapse–and in turn, becoming a black hole–by the quantum mechanical properties of the neutron-rich material that composes it.

An artist’s impression of a pulsar. (Michael Kramer/JBCA/Unversity of Manchester).

The finding may have implications that go beyond the modelling of neutron stars. Tiny deformations on the surface of rapidly spinning neutron stars called pulsars could launch gravitational waves–the tiny ripples in spacetime predicted by general relativity and detected here on Earth by the LIGO/Virgo collaboration.

Unfortunately, as precise and sensitive as the LIGO laser interferometer is, it is still not powerful enough to detect gravitational waves launched by these ant-hill like mountains. It is possible that future upgrades to these Earth-based detectors and advancements such as the space-based gravitational wave detector LISA could make observing the effect of these tiny bumps possible.

Hubble captures mind blowing footage of stars unleashing supersonic jets

Using 14 years of images put together, astronomers have managed to animate the fantastic chaos that takes place inside the supersonic jets of newborn stars.

Using pictures taken from 1994 to 2008 and a little image animation, NASA astronomers managed to put together these videos of supersonic jets being ejected out of stars.

“We’r trying to study how stars form. Just by looking at any one process, you don’t get the full picture,” said astronomer Patrick Hartigan of Rice University, who led a study using the new imagery published July 20 in Astrophysical Journal. “It’s very important to understand [the jets], because that’s how our sun formed, and that’s how planetary systems form. And that’s basically how we got here.”

What we’re looking at here is high speed jets shooting out from pulsars, black holes, stellar nurseries, and other galactic objects, all of which are at least 1350 light years away from our galaxy.

“It’s a lot like the difference between simply, say, looking at picture of … a quarterback throwing a pass versus actually seeing the entire play,” Hartigan said. “[It] really gives you the only way to get true insight into the physics of the dynamics of what’s going on.”

We now know the birth place of the biggest guitar in the galaxy

guitarIn case you’re wondering, the biggest ‘guitar’ in our galaxy is in fact a pulsar that was nicknamed The Guitar Pulsar. It’s basically a stellar corpse that emits a beam of electromagnetic radiation that just shreds interstellar gas, creating a wake of hot hydrogen shaped just like a guitar.

Little is known about these remnants, from any point of view. In order to track down it’s birthplace, Nina Tetzlaff at the University of Jena in Germany and her colleagues calculated the location of 140 groups of stars, as they were 5 millions ago.

The pulsar was practically launched from a cluster of massive stars, moving at about 1500 kilometres per second, which is just huge. They were able to pinpoint the exact location it was formed, but why it moved so fast still remains a mystery. Speeds over 1000 km/s are practically not used in current astronomy models, and are considered by many to be borderline impossible.

Nasa discovers a dozen pulsars that change understanding about dying stars

Recently, NASA’s Fermi Gamma-ray Space Telescope discovered no more, no less than 12 pulsars, and it also detected gamma ray pulse from 18 others. These findings are forcing scientists to rethink what we know about dying stars, as they totally underestimated the power of these stellar cilinders.

“We know of 1,800 pulsars, but until Fermi we saw only little wisps of energy from all but a handful of them,” says Roger Romani of Stanford University, Calif. “Now, for dozens of pulsars, we’re seeing the actual power of these machines.”

Pulsars are rotating neutron stars, highly magnetized, that emit a beam of electromagnetic radiation with a period of the pulse variating from 8.5 seconds to just 1.5 miliseconds. They are what remains when a massive star explodes. They’re also incredible cosmic dynamos and despite the fact that scientists don’t fully understand this process, they can say for sure that very intense electric and magnetic fields spin and accelerate particles to speeds very close to that of light.

Most pulsars were found because they emitted pulses at radio wavelength which are emitted from the pulsar’s poles. If these poles and the star’s spin axis are not alligned exactly, then the beams would be swept across the sky, meaning that we can detect them only if such a beam meats a radio telescope. But data is often inaccurate or biased because these telescopes are situated on Earth

“That has colored our understanding of neutron stars for 40 years,” Romani says. The radio beams are easy to detect, but they represent only a few parts per million of a pulsar’s total power. Its gamma rays, on the other hand, account for 10 percent or more. “For the first time, Fermi is giving us an independent look at what heavy stars do. “

“We used to think the gamma rays emerged near the neutron star’s surface from the polar cap, where the radio beams form,” addsAlice Harding of NASA’s Goddard Space Flight Center in Greenbelt, Md. “The new gamma-ray-only pulsars put that idea to rest.”

Now, scientists have their hands full with this new class of gamma-ray pulsars, which they believe arise far above the neutron star. Due to the fact that rotation powers their emissions they tend to slow down a bit as they “age”; however, Fermi picked up emissions from gamma rays from seven millisecond pulsars (which are called this way because they spin somewhere between 100 and 1000 times a second!!!). They tend to sometimes “break the rules”, and “cohabitate” with a normal star, residing in binary systems.

Here are some animations to give you a better and more visual understanding of this.

Quick Time animation
Credit: NASA/Fermi/Cruz deWilde

These gamma-ray pulsars show that gamma rays must form in a broader region than believed previously. Here, you can see the radio beams (green) never intersect Earth, but the pulsed gamma rays (magenta) do.


Animation 2
Credit: NASA/Goddard Space Flight Center Conceptual Image Lab


But gamma ray pulsars are no longer lighthouses, as pointed out here.


Animation 3
Credit: NASA/Dana Berry

Isolated pulsars slowly slow down their spin, but if a pulsar “lives” in a binary system with a normal star, it actually goes faster and faster. As a result, you could have a pulsar that spins in just a few miliseconds. How fast can they go?? It’s still uncertain.