Nav: Home

Beaming with the light of millions of suns

February 26, 2018

In the 1980s, researchers began discovering extremely bright sources of X-rays in the outer portions of galaxies, away from the supermassive black holes that dominate their centers. At first, researchers thought these cosmic objects, called ultraluminous X-ray sources, or ULXs, were hefty black holes with more than ten times the mass of the sun. But observations beginning in 2014 from NASA's NuSTAR and other space telescopes are showing that some ULXs, which glow with X-ray light equal in energy to millions of suns, are actually neutron stars -- the burnt-out cores of massive stars that exploded. Three such ULXs have been identified as neutron stars so far.

Now, a Caltech-led team using data from NASA's Chandra X-ray Observatory has identified a fourth ULX as being a neutron star -- and found new clues about how these objects can shine so brightly.

Neutron stars are extremely dense objects -- a teaspoon would weigh about a billion tons, or as much as a mountain. Their gravity pulls surrounding material from companion stars onto them, and as this material is tugged on, it heats up and glows with X-rays. But as the neutron stars "feed" on the matter, there comes a time when the resulting X-ray light pushes the matter away. Astronomers call this point -- when the objects cannot accumulate matter any faster and give off any more X-rays -- the Eddington limit.

"In the same that we can only eat so much food at a time, there are limits to how fast neutron stars can accrete matter," says Murray Brightman, a postdoctoral scholar at Caltech and lead author of a new report on the findings in Nature Astronomy. "But ULXs are somehow breaking this limit to give off such incredibly bright X-rays, and we don't know why."

In the new study, the researchers looked at a ULX in the Whirlpool galaxy, also known as M51, which lies about 28 million light-years away. They analyzed archival X-ray data taken by Chandra and discovered an unusual dip in the ULX's light spectrum. After ruling out all other possibilities, they figured out that the dip was from a phenomenon called cyclotron resonance scattering, which occurs when charged particles -- either positively charged protons or negatively charged electrons -- circle around in a magnetic field. Black holes don't have magnetic fields and neutron stars do, so the finding revealed that this particular ULX in M51 had to be a neutron star.

Cyclotron resonance scattering creates telltale signatures in a star's spectrum of light and the presence of these patterns, called cyclotron lines, can provide information about the strength of the star's magnetic field--but only if the cause of the lines, whether it be protons or electrons, is known. The researchers don't have a detailed enough spectrum of the new ULX to say for certain.

"If the cyclotron line is from protons, then we know that these magnetic fields around the neutron star are extremely strong and may in fact be helping to breaking the Eddington limit," says Brightman. Such strong magnetic fields could reduce the pressure from a ULX's X-rays -- the pressure that normally pushes away matter -- allowing the neutron star to consume more matter than what is typical and shine with the extremely bright X-rays.

If the cyclotron line is from circling electrons, in contrast, then the magnetic field strength around the neutron star would not be exceptionally strong, and thus the field is probably not the reason these stars break the Eddington limit. To further address the mystery, the researchers are planning to acquire more X-ray data on the ULX in M51 and look for more cyclotron lines in other ULXs.

"The discovery that these very bright objects, long thought to be black holes with masses up to 1,000 times that of the sun, are powered by much less massive neutron stars, was a huge scientific surprise," says Fiona Harrison, Caltech's Benjamin M. Rosen Professor of Physics; the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy; and the principal investigator of the NuSTAR mission. "Now we might actually be getting firm physical clues as to how these small objects can be so mighty."
The Nature Astronomy study, titled "Magnetic field strength of a neutron-star-powered ultraluminous X-ray source," was funded by NASA and the Ernest Rutherford Fellowships. Other authors include F. Fürst of the European Space Astronomy Centre; M.J. Middleton of University of Southampton, United Kingdom; D.J. Walton and A.C. Fabian of University of Cambridge, United Kingdom; D. Stern of NASA's Jet Propulsion Laboratory; M. Heida of Caltech; D. Barret of France's Centre national de la recherche scientifique and University of Toulouse; and M. Bachetti of Italy's Istituto Nazionale di Astrofisica.

California Institute of Technology

Related Magnetic Field Articles:

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.
Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.
New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.
Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.
Adhesive which debonds in magnetic field could reduce landfill waste
Researchers at the University of Sussex have developed a glue which can unstick when placed in a magnetic field, meaning products otherwise destined for landfill, could now be dismantled and recycled at the end of their life.
Earth's last magnetic field reversal took far longer than once thought
Every several hundred thousand years or so, Earth's magnetic field dramatically shifts and reverses its polarity.
A new rare metals alloy can change shape in the magnetic field
Scientists developed multifunctional metal alloys that emit and absorb heat at the same time and change their size and volume under the influence of a magnetic field.
Physicists studied the influence of magnetic field on thin film structures
A team of scientists from Immanuel Kant Baltic Federal University together with their colleagues from Russia, Japan, and Australia studied the influence of inhomogeneity of magnetic field applied during the fabrication process of thin-film structures made from nickel-iron and iridium-manganese alloys, on their properties.
'Magnetic topological insulator' makes its own magnetic field
A team of U.S. and Korean physicists has found the first evidence of a two-dimensional material that can become a magnetic topological insulator even when it is not placed in a magnetic field.
Scientists develop a new way to remotely measure Earth's magnetic field
By zapping a layer of meteor residue in the atmosphere with ground-based lasers, scientists in the US, Canada and Europe get a new view of Earth's magnetic field.
More Magnetic Field News and Magnetic Field Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Meditations on Loneliness
Original broadcast date: April 24, 2020. We're a social species now living in isolation. But loneliness was a problem well before this era of social distancing. This hour, TED speakers explore how we can live and make peace with loneliness. Guests on the show include author and illustrator Jonny Sun, psychologist Susan Pinker, architect Grace Kim, and writer Suleika Jaouad.
Now Playing: Science for the People

#565 The Great Wide Indoors
We're all spending a bit more time indoors this summer than we probably figured. But did you ever stop to think about why the places we live and work as designed the way they are? And how they could be designed better? We're talking with Emily Anthes about her new book "The Great Indoors: The Surprising Science of how Buildings Shape our Behavior, Health and Happiness".
Now Playing: Radiolab

The Third. A TED Talk.
Jad gives a TED talk about his life as a journalist and how Radiolab has evolved over the years. Here's how TED described it:How do you end a story? Host of Radiolab Jad Abumrad tells how his search for an answer led him home to the mountains of Tennessee, where he met an unexpected teacher: Dolly Parton.Jad Nicholas Abumrad is a Lebanese-American radio host, composer and producer. He is the founder of the syndicated public radio program Radiolab, which is broadcast on over 600 radio stations nationwide and is downloaded more than 120 million times a year as a podcast. He also created More Perfect, a podcast that tells the stories behind the Supreme Court's most famous decisions. And most recently, Dolly Parton's America, a nine-episode podcast exploring the life and times of the iconic country music star. Abumrad has received three Peabody Awards and was named a MacArthur Fellow in 2011.