When you look up at the stars, what do you imagine?
Probably giant balls of fire, much bigger than our planet, and often times, much bigger than our sun. What if I told you there were stars out there that have solid surfaces almost as smooth as glass, that are smaller than some clouds on Earth?
Neutron stars are a true spectacle to behold,
and they're nothing like the "normal" stars we learned about as kids. First of all, they're tiny, usually barely larger than 10 miles in diameter... Their size can be very misleading, though, as neutron stars are some of the most dense objects we've ever seen, and pack an enormous amount of mass into such a small space. They are essentially dying, cooling corpses of stars that were around 10 to 29 times as massive as our own sun, before they went supernova. Due to the conservation of angular momentum, neutron stars spin incredibly rapidly, and some neutron stars can rotate hundreds of times per second . When these stars retire, they live out the rest of their existence as exotic wonders, and their uniqueness can even serve as a galactic GPS!
It's not technically a single atom, but they may as well be.
When a star of sufficient mass (again, between 10 and 29 solar masses) comes to the end of its fusion cycle, it will begin to collapse inward, and create a supernova explosion, expelling its outer layers into space.
Neutron Star RCW 103, and the remnant of the supernova that created it, taken by the Chandra X-Ray telescope. Credit: NASA
Gravitational collapse gains traction with the supernova, and crushes the remaining core past the density of white dwarfs all the way down to the same density as an atomic nucleus! This pressure makes electrons and protons fuse into neutrons, giving the star its name. The atoms at the surface of a neutron star are so tightly packed that they are crushed into a solid lattice, creating a crust about a mile thick, so smooth it only varies by about 5mm...
Deeper into the star, atoms with many more neutrons are found. These elements would quickly decay somewhere like Earth, but because of the incredible pressure they are under, they remain stable. Who knows what sort of yet undiscovered elements might exist only within these stellar oddities? Deeper still, the size of individual atoms begins to decrease as gravity overcomes the strong force that binds atoms together. The core is thought to be made of free-flowing quarks, under so much pressure, they can't even form the fundamental particles that make up normal matter.
Hefty! Hefty! Hefty!
Despite their size, neutron stars usually contain about twice as much mass as our sun. Much bigger, and it would collapse into a black hole. All that mass packed into such a small space can be hard to fathom. To put it into perspective, a common explanation says that a single teaspoon of matter from a neutron star would weigh about 10 million tons on Earth. That's almost as much as 900 times the weight of the Great Pyramid of Giza!
All that mass creates an awful lot of gravity...
Like, 100 billion times as much gravity as Earth! This means if you were to stand on the surface of a neutron star, every atom in your body would break into their component particles. Even if you had a rocket that could resist that sort of pressure, in order to escape the star, you would need to launch away at nearly half the speed of light! If you fell from just 1 meter above the surface, it would only take a microsecond, and you'd hit the surface at nearly 3 million miles per hour.
Light dilation around a neutron star. Source
That much gravity causes strange effects on everything around it, including light. Looking at a neutron star, you can actually see more than half its surface because of the way gravity bends light. The light from an object like a planet behind the star would dilate around it, as portrayed in the image to the right. This means we would actually be able to see things directly behind the star that we normally wouldn't because of the star being in the way...
Beacons, and magnets, and quarks, oh my!
Neutron stars are classified in a few different ways, depending on observed properties like whether they have a partner, their magnetic field, and their ability to eject bright jets of material from their poles.
- Pulsars
Many neutron stars are observed to emit jets of radiation that stretch out into the depths of space. Pulsars were first observed about 50 years ago by their regularly timed radio emissions as the beams of energy sweep across the cosmos with the star's rapid rotation. These "pulses" of energy are unique. No two neutron stars spin at the same rate, allowing astronomers to use these spinning beacons of light as an sort of interstellar GPS that can be communicated across languages, and maybe even to other forms of intelligent life that may happen across the Voyager spacecraft... The fastest spinning neutron star we've observed to date, eloquently dubbed PSR J1748-2446ad, completes a rotation a little more than 700 times per second, and at it's equator, is spinning at around a quarter of the speed of light! Any neutron star that emits a beam of energy is considered a pulsar, even our next subject, the powerful...
- Magnetar
Artist's depiction of a magnetar. Source
All neutron stars have incredibly strong magnetic fields, but magnetars hold the crown for being the strongest magnets in the galaxy, with magnetic fields quadrillions of times stronger than Earth's! The mass density of even just the magnetic field around these beasts is 10,000 times that of lead... Crazy, but even crazier still are a couple last types of neutron stars that haven't been observed yet, but are theorized to exist.
- Quark stars & Preon stars
Source
Astronomers theorize that beyond the density of neutron stars, stars made up almost entirely of quarks. Quark stars are thought to be much smaller than neutron stars, and just a bit more dense, while preon stars are the beginning of black holes, or may even be black holes... preon stars pack much more mass into a space just minuscule fraction of the size, just around 10 centimeters !
Is your mind sufficiently blown for one day?
If you just can't get enough, read more about the immense power of neutron stars, like starquakes and neutron star collisions!
I hope you enjoyed reading this installment of Super Cool Science S#!t! I apologize for the length, but neutrons stars are just so damned awesome, I could have written another 2000 words on the subject easy!
References:
- https://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html
- https://www.space.com/22180-neutron-stars.html
- https://en.wikipedia.org/wiki/Neutron_star
