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Pulsar Glitches Help to Weigh a Star

By Dave Reneke

Pulsar glitches help to weigh a star, and Jupiter’s Great Red Spot is shrinking.

Researchers from the University of Southampton have developed a new method for measuring the mass of pulsars, highly magnetised rotating neutron stars formed from the remains of massive stars after they explode into supernovae.

Until now, scientists have determined the mass of stars, planets and moons by studying their relative motion using gravitational interactions between the two as the basis for their calculations. Southampton mathematicians have now found a new way to measure the mass of young pulsars using the principles of nuclear physics, rather than gravity, to work out their mass.

All previous precise measurements of pulsar masses have been made for stars that orbit another object, using the same techniques used to measure the mass of the Earth or Moon. This new technique is so different it can even be used for pulsars in isolation.

Pulsars emit a rotating beam of electro­magnetic radiation, which can be detected by telescopes when the beam sweeps past the Earth like the beam of a lighthouse. Renowned for their incredible rotational stability, young pulsars occasionally experience so-called “glitches” where they speed up for a very brief period of time.

It’s believed these glitches arise as a rapidly spinning superfluid within the star transfers its rotational energy to the star’s crust, the component that is tracked by observations.

Imagine the pulsar as a bowl of soup, with the bowl spinning at one speed and the soup spinning faster. Friction between the inside of the bowl and the soup will cause the bowl to speed up. The more soup there is, the faster the bowl will be made to rotate.

Lead researcher, Dr Wynn Ho, has collaborated with his colleagues to use new radio and X-ray data to develop a novel mathematical model that can be used to measure the mass of pulsars that glitch.

The magnitude and frequency of the pulsar glitches depend on the amount of superfluid in the star and the vortices within. By combining observational information with the nuclear physics involved, one can determine the mass of the star.

The team’s results have important implications for the next generation of radio telescopes like the Square Kilometre Array and the Low Frequency Array. The discovery and monitoring of many more pulsars is one of the key scientific goals of these and other similar projects.

Jupiter’s Great Red Spot Is Shrinking

A broad range of features have been captured in new images of Jupiter, including winds, clouds and storms. The scientists behind the new images took pictures of Jupiter using Hubble’s Wide Field Camera over a 10-hour period, producing two maps of the entire planet. These maps make it possible to determine the speed of Jupiter’s winds, to identify different phenomena in its atmosphere and to track changes in its most famous features.

The images confirm that the huge storm that has raged on Jupiter’s surface for at least 300 years continues to shrink. The storm, known as the Great Red Spot, is seen swirling at the centre of the image of the planet. It has been decreasing in size for some time but now the rate of shrinkage seems to be slowing again, even though the spot is still about 240 km smaller than it was in 2014.

At the centre of the spot, which is less intense in colour than it once was, is an unusual twisted, wispy filament spanning almost the entire width of the vortex. It’s distorted by winds that are blowing at a massive 540 km/h.

Another feature of interest, just north of the planet’s equator, is a rare wave structure, spotted on the planet only once before by the Voyager 2 spacecraft decades ago. Astronomers began to think its appearance was a fluke as nothing like it has been seen since – until now.

The current wave was found in a region dotted with cyclones and anticyclones. Similar waves called baroclinic waves sometimes appear in the Earth’s atmosphere where cyclones are forming. The wave may originate in a clear layer beneath the clouds, only becoming visible when it propagates up into the cloud deck.

A collection of maps will now be built up over time to help scientists not only understand the atmospheres of giant planets in the Solar System, but our own planet and of the planets that are being discovered around other stars.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com