Sometimes stars explode.
Good thing too. We owe our lives to the fact that heavy elements like iron and calcium are scattered into the Universe by exploding stars. Your blood and bones are the only things that exist because of it.
There are many different types of explosions. Astronomers have dubbed the new micronova a nova, because it is the first one they have discovered. Don't let the name fool you. This is still a brain-vaporizing event, because when it comes to astronomy, small is a very, very relative term.
novae is so bright that a new star appears in the sky, which was originally called nova stella.
After billions of years of existence, a star like the Sun will blow off its outer layers and reveal its core to space. If the original star was bigger, the white dwarf could have a significant fraction of the Sun's mass in it. The surface gravity of a white dwarf can be over a hundred thousand times that of Earth.
If it is in a pair of stars, the material from one can be sucked off by the other. It falls onto the ground. The gravity is so strong that once the hydrogen piles up, it gets compressed enough to undergo thermonuclear fusion, releasing a huge amount of energy, tens or even hundreds of thousands of times the Sun's luminosity.
The white dwarf settles down again after a brief eruption in which material is blasted away into space. Sometimes the pattern repeats and we get a nova. Sometimes the hydrogen falls onto the star at the right rate that it really piles up, and when it suddenly fails, enough energy is released to tear the star apart. For a few weeks, this supernova can surpass all the other stars in a galaxy, billion of times brighter than the Sun.
That is at the top end of the scale. There is a beastie at the lower end. It was discovered by an observatory.
The TESS scans the entire sky, sector by sector, making careful measurements of the brightness of hundreds of thousands of stars. It is looking for the mini-eclipses caused by a planet passing in front of its host star, a method so successful it has been used to find the vast majority of all exoplanets.
It's not picky, and can see all the stars, including white dwarfs. It is able to spot changes in brightness that might occur on short timescales because it takes measurements over and over.
Three white dwarfs underwent bursts of rapid brightening when looking at TESS data. The three are all from their stellar companions. The novae bursts were very fast, peaking in about an hour and taking around 10 hours to fade.
The energy released was a millionth of what a nova would be. What causes them?
Magnetic confinement! White dwarfs can have strong magnetic fields. The material is so hot that the atoms have lost electrons. Magnetic fields can affect them when that happens. A white dwarf's magnetic field is shaped like a doughnut, coming out at one pole and going back in at the other. The ionized material from the other star goes to the white dwarf's poles.
When a nova explodes, the material can spread all over the star's surface, making it a global event. The magnetic fields can act like a force field if they are configured correctly. The amount of material in a nova is much higher than in a thermonuclear fusion event. There was a boom. Or boom. Micronova.
The TESS observations of the three white dwarfs make for strong evidence that this is what it is. Micro novae can take months or mere days to blow up again, unlike regular novae which take years to build up material.
The bang is still strong, releasing as much energy as the Sun in a few hours. The Sun's luminosity is equivalent to exploding 100 billion one-megaton bombs every second. The amount of hydrogen fused in the event is 40 quadrillion tons, which is difficult to comprehend. That is equal to a couple of hundred thousand times the mass of Mount Everest.
The reason these were not seen is because we are now looking at the sky in new ways. We have big observatories that are much deeper in the sky and can see fainter objects as well. These innovations allow us to find objects that we couldn't see before.
One thing any astronomer will tell you is that when we look at the sky in new ways, we see new things. That means we learn more.
The whole point is that.
All Rights Reserved © 2024
