Getting too close to a black hole is bad news. The black hole’s gravity can pull apart anything that’s falling into it atom by atom. A magnetar can do the same thing. And it’s not just its gravity you have to worry about. Its magnetic field can do the job as well – from hundreds of miles away.
A magnetar is a neutron star -the crushed corpse of a once mighty star. It’s heavier than the Sun, but only a little bigger than Washington, D.C. It’s born when a massive star can no longer produce nuclear reactions in its core. The core collapses, while the star’s outer layers explode.
The original star generated a strong magnetic field. As the core collapsed, the field was mashed inward as well, making it extremely powerful. It’s boosted by the turbulent sloshing inside the newly formed neutron star. So a typical magnetar’s magnetic field is a million billion times the strength of Earth’s field.
The neutron star sticks around, but its magnetic field weakens in a hurry. So there aren’t many magnetars around – only about 30 have been discovered.
The magnetic field can help produce titanic explosions. Interactions with the field can cause the crust of a neutron star to crack in a “starquake.” Energy from the quake is beamed out by the magnetic field, producing an outburst of gamma rays. The most powerful quake yet seen generated more energy in a tenth of a second than the Sun will emit in 150,000 years – the enormous power of a magnetar.
More about neutron stars tomorrow.
Script by Damond Benningfield
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Neutron Stars
When the most massive stars die, they can leave behind two types of corpse. The heaviest ones probably form black holes. But the fate of the others is no less exotic. They form neutron stars – ultra-dense balls that are more massive than the Sun, but no bigger than a small city.
A massive star “dies” when its core can no longer produce nuclear reactions. For a star of about eight to 20 or more times the mass of the Sun, the core collapses, while the star’s outer layers explode as a supernova.
The gravity of the collapsing core squishes together protons and electrons to make neutrons – particles with no electric charge. The neutrons can be squished together only so much before they halt the collapse. By then, the core is trillions of times as dense as Earth. So a chunk of a neutron star the size of a sugar cube would weigh as much as a mountain.
A neutron star probably has a solid crust made of iron or other elements, with no features more than a couple of millimeters tall.
The gravity at the center of a neutron star is so strong that we don’t really know what the conditions are like – there’s just nothing to compare it to.
There could be as many as a billion neutron stars in the galaxy. But they’re hard to find. Some of them make it a little easier, though. They produce the most powerful magnetic fields in the universe – and some of the most powerful outbursts. More about that tomorrow.
Script by Damond Benningfield
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Speedy Star
You can always count on the constellations. Over the course of a human lifetime, their configuration doesn’t change – they don’t appear to move at all.
That’s an illusion, though. The stars are all so far away that we don’t see any motion. But they’re all moving in a hurry. And one of the fastest is in view on autumn evenings.
Gamma Piscium is the second-brightest member of Pisces, the fishes. The constellation stretches across the east and southeast at nightfall. Gamma Piscium is near its top right corner – part of a pentagon of faint stars.
Gamma Piscium is a giant. It’s nearing the end of its life, so it’s getting bigger and brighter. Right now, it’s about 10 times the diameter of the Sun, and more than 60 times the Sun’s brightness. That makes it faintly visible to the eye alone, even though it’s 135 light-years away.
Perhaps the most interesting fact about Gamma Piscium is its speed: It’s moving through the galaxy at about 340,000 miles per hour – faster than all but a few other visible stars. At that rate, it’ll move the equivalent of the Moon’s diameter in less than 3,000 years.
The star’s composition hints that it came from outside the disk of the Milky Way – the part of the galaxy that includes the Sun. The star has very few heavy elements. That suggests it formed outside the disk, and just happens to be passing by – zipping through the galaxy like a speeding rocket.
Script by Damond Benningfield
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Messier 30
An interloper from another galaxy scoots low across the south on October evenings. It’s a tight family of stars – hundreds of thousands of them. The stars probably belonged to another galaxy that was consumed by the Milky Way in the distant past.
Messier 30 is low in the south at nightfall, in Capricornus. The sea-goat’s brightest stars form a wide triangle. M30 is on the lower left side of the triangle
Messier 30 is a globular cluster – a ball of stars about 90 light-years wide. Most of the stars are concentrated in the cluster’s dense core. The numbers tail off as you move toward the cluster’s edge. Anything that wanders too far from the center gets yanked away by the gravity of the rest of the galaxy.
The Milky Way is home to more than 150 globular clusters. But several of them appear to have come from other galaxies. And that includes M30.
The main clue to its origin is its orbit. As it circles the center of the galaxy, M30 moves in the opposite direction from most of the stars and star clusters.
The only way for such a massive cluster to move against the traffic is if it came from outside the galaxy. So Messier 30 isn’t a native of the Milky Way. Instead, it was pulled in by the Milky Way’s powerful gravity – making it a refugee from another galaxy.
We’ll talk about an individual star that might be a refugee from another part of the galaxy tomorrow.
Script by Damond Benningfield
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Uranus Opposition IV
If you’ve ever left a can of soda in the freezer for too long, you can appreciate what happened to the largest moon of the planet Uranus: It cracked.
Titania is almost a thousand miles in diameter – less than half the size of our moon. But it orbits Uranus at about the same distance as the Moon does from Earth. And like the Moon, it’s locked in such a way that the same hemisphere always faces its planet.
When Titania was born, its interior was warm. But it quickly froze. As it did so, the surface cracked, creating some impressive canyons. The largest is a network known as Messina Chasma. Like Titania itself, it’s named for a character from Shakespeare – in this case, from “A Midsummer Night’s Dream`.”
The canyons are more than 900 miles long, wrapping from the equator to near the south pole. They’re up to 60 miles wide, and miles deep. Few impact craters have scarred Messina, indicating that it’s fairly young.
In fact, Titania’s entire surface appears to be younger than those of Uranus’s other big moons. That doesn’t mean the moon itself is younger. Instead, it probably was repaved by ice flowing from inside – resetting the clock for this fractured moon.
Uranus is in view all night, in Taurus. And it’s closest to Earth for the year – 1.7 billion miles away. Despite the distance, it’s big enough that it’s an easy target for binoculars. But you need a decent telescope to see Titania.
Script by Damond Benningfield
USA