NEWS | May 18, 2017

Neutron Stars Are Weird!

There, we came right out and said it. They can’t help it; it’s just what happens when you have a star that’s heavier than our Sun but as small as a city. Neutron stars give us access to crazy conditions that we can’t study directly on Earth.

Here are five facts about neutron stars that show sometimes they are stranger than science fiction!

1. Neutron stars start their lives with a bang

This visualization opens on a star field with a bright star at the center of the image. The star then explodes, filling the frame with white light for a moment. As that bright light fades, we see there is a bubble of yellow and red material expanding away from the site of the exploded star.
When a star that is eight times larger than the Sun ends its life, it does not go gentle into that good night. Shifting pressure in its core causes it to collapse and trigger a supernova, the one of the largest explosions in the universe. The initial flash of light, which can outshine the star’s host galaxy, may last only seconds. But the resulting debris that is flung into space can be studied for millennia. Credit: Courtesy of ESA/Hubble/L. Calçada

When a star bigger and more massive than our Sun runs out of fuel at the end of its life, its core collapses while the outer layers are blown off in a supernova explosion. What is left behind depends on the mass of the original star. If it’s roughly 7 to 19 times the mass of our Sun, we are left with a neutron star. If it started with more than 20 times the mass of our Sun, it becomes a black hole.

2. Neutron stars contain the densest material that we can directly observe

An imagined neutron star hangs over San Francisco. The blue and black ball spins just above the clouds.
This animation shows the size and scale of a neutron star over San Francisco. Neutron stars squeeze up to two solar masses into a city-size volume, giving rise to the highest stable densities known anywhere. The nature of matter under these conditions is a decades-old unsolved problem. Credit: NASA's Goddard Space Flight Center/Conceptual Image Lab

While neutron stars’ dark cousins, black holes, might get all the attention, neutron stars are actually the densest material that we can directly observe. Black holes are hidden by their event horizon, so we can’t see what’s going on inside. However, neutron stars don’t have such shielding. To get an idea of how dense they are, one sugar cube of neutron star material would weigh about 1 trillion kilograms (or 1 billion tons) on Earth – about as much as a mountain. That is what happens when you cram a star with up to twice the mass of our Sun into a sphere the diameter of a city.

3. Neutron stars can spin as fast as blender blades

A mottled blue and black ball, representing a neutron star, spins about once per second. There are light blue ovals on opposite sides of the neutron star representing hotspots on its surface that are offset from the spin axis. From each oval is a beam of light extending from the oval out of the frame. As the star spins, the hotspots and beams come in and out of our view, making it look like the star is pulsing.
Animation of a spinning neutron star in space. Neutron stars are directly observable, usually as “pulsars” – the lighthouses of the cosmos. Credit: NASA's Goddard Space Flight Center/Conceptual Image Lab

Some neutron stars, called pulsars, emit streams of light that we see as flashes because the beams of light sweep in and out of our vision as the star rotates. The fastest known pulsar, named PSR J1748-2446ad, spins 43,000 times every minute. That’s twice as fast as the typical household blender! Over weeks, months or longer, pulsars pulse with more accuracy than an atomic clock, which excites astronomers about the possible applications of measuring the timing of these pulses.

4. Neutron stars are the strongest known magnets

A yellow ball spins at the center of the image, representing a neutron star. The magnetic field lines are visualized as electric blue lines that spin with the star. The lines start near the top of the sphere, arc out into space, landing back on the bottom of the sphere. The field lines closest to the top of the neutron star spill off the screen.
This animation takes us into a spinning pulsar, with its strong magnetic field rotating along with it. Clouds of charged particles move along the field lines and their gamma rays are beamed like a lighthouse beacon by the magnetic fields. As our line of sight moves into the beam, we see the pulsations once every rotation of the neutron star. Credit: NASA's Goddard Space Flight Center/Conceptual Image Lab

Like many objects in space, including Earth, neutron stars have a magnetic field. While all known neutron stars have magnetic fields billions and trillions of times stronger than Earth’s, a type of neutron star known as a magnetar can have a magnetic field another thousand times stronger. These intense magnetic forces can cause starquakes on the surface of a magnetar, rupturing the star’s crust and producing brilliant flashes of gamma rays so powerful that they have been known to travel thousands of light-years across our Milky Way galaxy, causing measurable changes to Earth’s upper atmosphere.

5. Neutron stars’ pulses were originally thought to be possible alien signals

A star shown in purple at the center of this starfield pulses, quickly getting brighter and dimmer.
A pulsar is a neutron star which emits beams of radiation that sweep through Earth's line of sight. The "pulses" of high-energy radiation we see from a pulsar, shown in this animation, are due to a misalignment of the neutron star's rotation axis and its magnetic axis. External viewers see pulses of radiation whenever this region above the magnetic pole is visible. Credit: NASA's Goddard Space Flight Center

Beep. Beep. Beep. The discovery of pulsars began with a mystery in 1967 when astronomers picked up very regular radio flashes but couldn’t figure out what was causing them. The early researchers toyed briefly with the idea that it could be a signal from an alien civilization, an explanation that was discarded but lingered in their nickname for the original object – LGM-1, a nod to the “little green men” (it was later renamed PSR B1919+21). Of course, now scientists understand that pulsars are spinning neutron stars sending out light across a broad range of wavelengths that we detect as very regular pulses – but the first detections threw observers for a loop.

This animation starts on a wide shot of the International Space Station and zooms in to the location where the NICER payload is found. NICER is a box-shaped instrument that connects to the space station with a single arm, and it swivels in this animation, showing how it can point to different objects in the sky.
This animation shows a wide-angle view and zoom in of the NICER payload onboard the International Space Station. Credit: NASA's Goddard Space Flight Center/Conceptual Image Lab

Our Neutron star Interior Composition Explorer (NICER) payload on the International Space Station is giving astronomers more insights into neutron stars – helping us determine what is under the surface.

Want to learn even more about neutron stars? Watch this …

This video explains some of what's known about neutron stars and previews NASA's Neutron star Interior Composition Explorer mission (NICER). Credit: NASA's Goddard Space Flight Center

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