Association of Universities for Research in Astronomy
An artist's impression of a white dwarf and a millisecond pulsar. The first example of a white dwarf and a pulsar in a system was discovered by using the 4.1-meter Telescope on Cerro Pachn. The missing link in the evolution of such systems is the source. Credit: NOIRLab, AURA, J. da Silva, and Spaceengine.
Astronomers using the 4.1-meter Telescope in Chile have discovered the first example of a star in the process of becoming a white dwarf and a neutron star that is spinning into a pulsar. The pair is a missing link in the evolution of such systems.
The source of the bright, mysterious source of gamma rays is a rapidly spinning neutron star that is in the process of evolving into an extremely-low-mass white dwarf. Astronomers refer to these types of systems asspiders because the pulsar tends to eat the outer parts of the companion star as it turns into a white dwarf.
The duo was detected using the 4.1-meter SOAR Telescope on Cerro Pachn, part of the Cerro Tololo Inter-American Observatory.
NASA's Fermi Telescope has been cataloging objects in the universe that produce a lot of gamma rays since it was launched in 2008, but not all of the sources of the rays have been classified. The second-brightest gamma-ray source in the entire sky, called 4FGL J1120.0-2206, was not known until now.
Astronomers from the US and Canada used the SOAR Telescope to determine the true identity of 4FGL J1120.0-2204. The system consisting of a "millisecond pulsar" that spins hundreds of times per second, has been shown to be the source of the gamma-ray source. The pair is located over 2500 light-years away.
Swihart says that the location of the SOAR Telescope, the precision and stability of the Goodman spectrograph and Michigan State University's dedicated time on the telescope were important aspects of the discovery.
Chris Davis, NOIRLab Program Director at the US National Science Foundation, says that this is a great example of how mid-sized telescopes can be used to help characterize unusual discoveries made with other ground and space-based facilities. The follow-up of many other time-variable and multi-messenger sources over the coming decade is anticipated to be helped by the SOAR.
The light from the white dwarf companion is shifted to the red and blue by the telescope, which shows that it is traveling around a massive star every 15 hours.
Swihart's team was able to take the properties of the companion star and apply them to models describing how the stars evolve. This allowed them to determine that the companion is the beginning of an extremely-low-mass white dwarf, with a surface temperature of 15000 F and a mass of just 18% of the sun.
When a star with a mass similar to that of the sun or less reaches the end of its life, it will run out of hydrogen used to fuel the nuclear fusion processes in its core. For a time, the star is powered by helium, which causes it to contract and heat up, leading to its evolution into a red giant that is hundreds of millions of kilometers in size. A white dwarf about the size of Earth can be left behind when the outer layers of this swollen star are fused onto a companion.
Astronomers using the 4.1-meter Telescope in Chile have discovered the first example of a star in the process of becoming a white dwarf and a neutron star that is spinning into a pulsar. The pair is a missing link in the evolution of such systems. Images and Videos: NOIRLab, AURA, J. da Silva, Spaceengine, and J. P. Burgos.
The dwarf in the 4FGL J1120.0-2206 system is evolving. Swihart says that it is five times larger in radius than normal white dwarfs. It will look similar to many of the extremely low mass white dwarfs that we already know about in about two billion years.
The pulsars twirl hundreds of times a second. The white dwarf is spun up by the accretion of matter from a companion. When the pulsar wind collides with material from a companion star, most millisecond pulsars emit X-rays and gamma rays.
An extremely low-mass white dwarf is the first one found that is likely to be around a neutron star. The tail-end of the spin-up process is looked at in 4FGL J1120.0-2204. The other white dwarf–pulsar binaries are past the spinning-up stage.
Swihart says that the companion was seen by using follow-up spectroscopy with the SOAR Telescope. Without those observations, we wouldn't have found this system.
This research was presented in a paper in The Astrophysical Journal.
There is a unique bright star with an extremely low mass.
The Association of Universities for Research in Astronomy (AURA) provided this.
The source of powerful gamma-rays was retrieved from a Cosmic Spider on January 12.
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