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[Music throughout]This is J0030, a type

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of dead star called a pulsar, located about 1,100 light-years

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away in the constellation Pisces. Observing

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J0030 in X-rays, astronomers have now made the most precise

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and reliable measurements of any pulsar’s size. And they’ve discovered

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that J0030's appearance differs dramatically from textbook depictions.

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NASA’s Neutron star Interior

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Composition Explorer, or NICER, is a telescope on the International

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Space Station. NICER makes extremely detailed X-ray measurements

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of neutron stars, and its data provided this unprecedented glimpse

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of J0030. A neutron star is the crushed

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core of a massive star that exploded in a supernova. Pulsars,

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like J0030, are rapidly spinning neutron stars

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that sweep beams of energy across our line of sight, much like a lighthouse.

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A pulsar is so dense that its gravity

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bends the fabric of space-time around it. NICER’s precise

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X-ray measurements allow scientists to take advantage of this effect

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to see light from the far side of the pulsar. This is

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a pulsar-sized object about 16 miles across but with much less

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mass. We only see light from the side of the object nearest

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to Earth. But as its mass increases, the object warps

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space-time and acts like a lens to show us light from the far side.

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This has the strange effect of making a pulsar look bigger than it really is.

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The more mass an object of a given size contains, the more

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it distorts space-time and the more we see of its far side.

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Textbooks show pulsars with two hot spots on the surface,

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directly opposite each other at the magnetic poles.

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As the pulsar spins, the spots come in and out of view, creating regular

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changes in its X-ray brightness. If the pulsar’s mass is

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low, the spots disappear when they rotate to the far side.

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But if the mass is high enough, the hot spots may never completely disappear.

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Using NICER data, two teams

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of scientists examined different models for the shapes, and even the number,

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of hot spots on J0030. Both

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arrived at the same conclusion — the pulsar is around 16 miles across

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and about 1.4 times the Sun’s mass.

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This represents the most precise measurement yet of a pulsar’s size,

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with an uncertainty of less than 10%. The spots themselves

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don’t match the textbook image, though. From Earth, we look down onto

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J0030’s northern hemisphere. Both teams say there are no

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spots there at all. Contrary to the simple magnetic dipole model,

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all the spots appear in the southern hemisphere and are not necessarily

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in shapes we might expect. One team, led by researchers

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at the University of Amsterdam, suggests J0030

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has one small circular spot and another long, crescent-shaped one.

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The other team, led by researchers at the Universities of

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Maryland and Illinois, finds two oval hot spots.

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Their sizes, shapes and locations closely match those derived from

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the other model. However, the Maryland-led team also finds

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a third, cooler spot located slightly askew

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of the pulsar’s south rotational pole, just at the edge of our view of the pulsar.

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Scientists are still trying to determine why

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J0030’s spots take on these shapes and arrangements, but for now it’s

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clear that pulsar magnetic fields are more complex than originally

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assumed. NICER’s measurements of

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J0030 have opened a new chapter in our understanding of neutron

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stars. As it continues to study other pulsars,

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we’ll learn even more about the common characteristics — and

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individual quirks — of these incredible objects.

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[Pulsar grid animations by Sharon Morsink, University of Alberta. Pulsar magnetosphere animation by Alice Harding, Constantinos Kalapotharakos, and Zorawar Wadiasingh, NASA’s Goddard Space Flight Center]

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[Pulsar grid animations by Sharon Morsink, University of Alberta. Pulsar magnetosphere animation by Alice Harding, Constantinos Kalapotharakos, and Zorawar Wadiasingh, NASA’s Goddard Space Flight Center]

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[Explore: solar system & beyond]

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