From AAS NOVA: “An Infant Pulsar Defies Categorization”

AASNOVA

From AAS NOVA

27 July 2020
Susanna Kohler

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Artist’s illustration of a magnetar, a neutron star with powerful magnetic fields. [ESA]

Pulsars have historically been classified into different categories — but the distinction between them may be blurrier than we thought. The discovery of the youngest pulsar yet observed is now raising questions about how we classify these extreme objects.

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Artist’s illustration of an accretion-powered pulsar (left) and its small stellar companion (right), viewed within their orbital plane. [NASA Goddard SFC/Cruz deWilde]

The Source of a Pulsar’s Power

When a massive star explodes as a supernova at the end of its lifetime, an incredibly dense remnant with the mass of one or two Suns — but spanning only 20 km or so in diameter — is left behind. If this resulting neutron star is powerfully magnetized, it can emit a beam of radiation that sweeps across the Earth as the star spins, appearing to us as a pulsar.

The pulsars that we’ve observed are classified into three categories based on what we think powers their emission:

Rotation-powered pulsars Usually detected from their pulsed radio emission, this is the most commonly observed type of pulsar. These rapidly rotating stars gradually spin down over time. Their lost rotational energy powers the particle acceleration that produces the emission we observe.
Accretion-powered pulsars These pulsars occur in binaries and accrete matter from their companion stars. Pulsed X-ray radiation is produced by rotating hot spots caused when the accretion flow strikes the surface of the pulsar.
Magnetically-powered pulsars These bodies, known as magnetars, are the most magnetized objects in the universe, sporting magnetic fields of around 1014–1015 Gauss (compare this to Earth’s magnetic field, which is less than one Gauss!). The decay of their unstable magnetic field powers the emission of high-energy radiation, particularly at X-ray and gamma-ray wavelengths.

But what if these pulsar categories aren’t as distinct as we think they are? Observations of a very recently born pulsar, described in a publication led by Paolo Esposito (Scuola Superiore IUSS and INAF, Italy), are now challenging our classifications.

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The source Swift J1818, as observed by the XMM-Newton spacecraft. [Adapted from Esposito et al. 2020]

ESA/XMM Newton

Neither Here Nor There

The source Swift J1818.0–1607 was first discovered in March 2020 as a flaring outburst of X-ray radiation. Esposito and collaborators present X-ray observations of the source using the Swift Observatory, XMM-Newton [above], and NuSTAR, all of which paint the picture of an incredibly young — just 240 years, a relative baby on cosmic scales! — magnetar undergoing an outburst.

NASA Neil Gehrels Swift Observatory

NASA/DTU/ASI NuSTAR X-ray telescope

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Profile of a bright radio pulse from the source Swift J1818, as observed by the Sardinia Radio Telescope. [Adapted from Esposito et al. 2020]

But Swift J1818 has its quirks. Of the roughly 30 magnetars we’ve discovered, Swift J1818 spins faster than any of them, with a period of just 1.36 seconds. Its quiescent luminosity is lower than we’d expect given its young age. And follow-up radio observations with the Sardinia Radio Telescope in Italy reveal that Swift J1818 also exhibits the strong and short radio pulses expected for a rotation-powered pulsar.

Sardinia Radio Telescope based in Pranu Sanguni, near Sant’Andrea Frius and San Basilio, about 35 km north of Cagliari (Sardinia, Italy), altitude 600 m (2,000 ft)

Esposito and collaborators’ observations lead them to conclude that Swift J1818 is a peculiar magnetar with properties that straddle those of rotationally and magnetically powered pulsars. This makes this newborn the latest in a small collection of oddball young neutron stars with diverse properties, suggesting that there may still be much we don’t know about the driving forces behind pulsar emission, and how this changes over a pulsar’s lifetime.

Citation

“A Very Young Radio-loud Magnetar,” P. Esposito et al 2020 ApJL 896 L30.
https://iopscience.iop.org/article/10.3847/2041-8213/ab9742

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Women in STEM – Dame Susan Jocelyn Bell Burnell Discovered pulsars.

Dame Susan Jocelyn Bell Burnell discovered pulsars with radio astronomy. Jocelyn Bell at the Mullard Radio Astronomy Observatory, Cambridge University, taken for the Daily Herald newspaper in 1968. Denied the Nobel.

Dame Susan Jocelyn Bell Burnell at work on first plusar chart 1967 pictured working at the Four Acre Array in 1967. Image courtesy of Mullard Radio Astronomy Observatory.

Dame Susan Jocelyn Bell Burnell 2009

Dame Susan Jocelyn Bell Burnell (1943 – ), still working from http://www. famousirishscientists.weebly.com

Biography

British astrophysicist, scholar and trailblazer Jocelyn Bell Burnell discovered the space-based phenomena known as pulsars, going on to establish herself as an esteemed leader in her field.Who Is Jocelyn Bell Burnell?
Jocelyn Bell Burnell is a British astrophysicist and astronomer. As a research assistant, she helped build a large radio telescope and discovered pulsars, providing the first direct evidence for the existence of rapidly spinning neutron stars. In addition to her affiliation with Open University, she has served as dean of science at the University of Bath and president of the Royal Astronomical Society. Bell Burnell has also earned countless awards and honors during her distinguished academic career.

Early Life

Jocelyn Bell Burnell was born Susan Jocelyn Bell on July 15, 1943, in Belfast, Northern Ireland. Her parents were educated Quakers who encouraged their daughter’s early interest in science with books and trips to a nearby observatory. Despite her appetite for learning, however, Bell Burnell had difficulty in grade school and failed an exam intended to measure her readiness for higher education.

Undeterred, her parents sent her to England to study at a Quaker boarding school, where she quickly distinguished herself in her science classes. Having proven her aptitude for higher learning, Bell Burnell attended the University of Glasgow, where she earned a bachelor’s degree in physics in 1965.

Little Green Men

In 1965, Bell Burnell began her graduate studies in radio astronomy at Cambridge University. One of several research assistants and students working under astronomers Anthony Hewish, her thesis advisor, and Martin Ryle, over the next two years she helped construct a massive radio telescope designed to monitor quasars. By 1967, it was operational and Bell Burnell was tasked with analyzing the data it produced. After spending endless hours pouring over the charts, she noticed some anomalies that did not fit with the patterns produced by quasars and called them to Hewish’s attention.

Over the ensuing months, the team systematically eliminated all possible sources of the radio pulses—which they affectionately labeled Little Green Men, in reference to their potentially artificial origins—until they were able to deduce that they were made by neutron stars, fast-spinning collapsed stars too small to form black holes.

Pulsars and Nobel Prize Controversy

Their findings were published in the February 1968 issue of Nature and caused an immediate sensation. Intrigued as much by the novelty of a woman scientist as by the astronomical significance of the team’s discovery, which was labeled pulsars—for pulsating radio stars—the press picked up the story and showered Bell Burnell with attention. That same year, she earned her Ph.D. in radio astronomy from Cambridge University.

However, in 1974, only Hewish and Ryle received the Nobel Prize for Physics for their work. Many in the scientific community raised their objections, believing that Bell Burnell had been unfairly snubbed. However, Bell Burnell humbly rejected the notion, feeling that the prize had been properly awarded given her status as a graduate student, though she has also acknowledged that gender discrimination may have been a contributing factor.

Life on the Electromagnetic Spectrum

Nobel Prize or not, Bell Burnell’s depth of knowledge regarding radio astronomy and the electromagnetic spectrum has earned her a lifetime of respect in the scientific community and an esteemed career in academia. After receiving her doctorate from Cambridge, she taught and studied gamma ray astronomy at the University of Southampton. Bell Burnell then spent eight years as a professor at University College London, where she focused on x-ray astronomy.

During this same time, she began her affiliation with Open University, where she would later work as a professor of physics while studying neurons and binary stars, and also conducted research in infrared astronomy at the Royal Observatory, Edinburgh. She was the Dean of Science at the University of Bath from 2001 to 2004, and has been a visiting professor at such esteemed institutions as Princeton University and Oxford University.

Array of Honors and Achievements

In recognition of her achievements, Bell Burnell has received countless awards and honors, including Commander and Dame of the Order of the British Empire in 1999 and 2007, respectively; an Oppenheimer prize in 1978; and the 1989 Herschel Medal from the Royal Astronomical Society, for which she would serve as president from 2002 to 2004. She was president of the Institute of Physics from 2008 to 2010, and has served as president of the Royal Society of Edinburgh since 2014. Bell Burnell also has honorary degrees from an array of universities too numerous to mention.

Personal Life

In 1968, Jocelyn married Martin Burnell, from whom she took her surname, with the two eventually divorcing in 1993. The two have a son, Gavin, who has also become a physicist.

A documentary on Bell Burnell’s life, Northern Star, aired on the BBC in 2007.


Dame Susan Jocelyn Bell Purnell at Perimeter Institute Oct 26, 2018.

See the full article here .


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