AR Scorpii
First white dwarf-pulsar binary discovered.
AR Scorpii is a binary star system located about 383 light-years away in the constellation Scorpius, near the ecliptic plane. It consists of a white dwarf that behaves like a pulsar and a red dwarf star. The system was first identified as a variable star in 1904 by Henrietta Swan Leavitt and Edward Charles Pickering, and it received its variable star designation in 1914.
AR Scorpii is the first known white dwarf pulsar. Its unusual nature was initially noticed by amateur astronomers. A 3.56-hour period in its light curve led to it being mistakenly classified as a Delta Scuti variable, but in 2016 this period was identified as the binary orbital period. The system also shows very strong optical, ultraviolet, and radio pulsations with a period of 1.97 minutes, originating from the red dwarf. This 1.97-minute period is a beat period between the orbital motion and the white dwarf's spin. These pulsations occur when a relativistic beam from the white dwarf sweeps across the red dwarf, which then converts the beam into the observed electromagnetic energy. Although the white dwarf shows evidence of past accretion, it is not currently accreting significantly; the system is powered by the white dwarf's spin-down, which will slow its rotation over a timescale of about 10 million years. The white dwarf has a radius of roughly 7,000 kilometers, similar to Earth's size.
- Distance
- 117.4 parsecs (383 light-years)
- Orbital period
- 3.56 hours
- Pulsation period
- 1.97 minutes
- White dwarf radius
- 7×10³ km
- Spin down timescale
- 10⁷ years
- Constellation
- Scorpius
- Discovery announcement
- 1904 by Henrietta Swan Leavitt and Edward Charles Pickering
Lore & Background
AR Scorpii was discovered as a variable star in 1904 by Henrietta Swan Leavitt and Edward Charles Pickering, and given its variable star designation in 1914. Its unusual nature was first noticed by amateur astronomers. The 3.56-hour period in its light curve caused it to be misclassified as a Delta Scuti variable, but in 2016 this period was identified as the binary orbital period.
The system shows very strong optical, ultraviolet, and radio pulsations originating from the red dwarf with a period of 1.97 minutes, which is a beat period from the orbital rotation and the white dwarf spin. These pulsations occur when a relativistic beam from the white dwarf sweeps across the red dwarf, which then reprocesses the beam into observed electromagnetic energy. Although the white dwarf shows evidence of past accretion, it is not accreting significantly at present, and the system is powered by the spin-down of the white dwarf. The white dwarf has a radius of about 7×10³ km, about the same size as Earth.
Reader's Guide
AR Scorpii holds significance as the first 'white dwarf-pulsar' discovered, marking a new class of binary system where a white dwarf exhibits pulsar-like behavior. Its discovery by amateur astronomers highlights the role of citizen science in modern astronomy. The system's 1.97-minute pulsations arise from a relativistic beam from the white dwarf sweeping across the red dwarf, which reprocesses the beam into optical, ultraviolet, and radio emissions. This mechanism differs from traditional pulsars, which involve neutron stars. The white dwarf's spin-down powers the system, with a timescale of 10⁷ years, and its radius is comparable to Earth's. The system's location near the ecliptic in Scorpius and its distance of 117.4 parsecs were determined via very-long-baseline interferometry. AR Scorpii's legacy includes providing a new laboratory for studying white dwarf magnetospheres and binary interactions, and it is often compared to AE Aquarii, the first discovered white dwarf pulsar.
Did You Know?
- AR Scorpii is the first discovered 'white dwarf-pulsar' binary system.
- Its 1.97-minute pulsations are a beat period from the orbital rotation and white dwarf spin.
Frequently Asked Questions
What is AR Scorpii?
AR Scorpii is a binary star system roughly 383 light-years from Earth, situated in the constellation Scorpius close to the ecliptic plane. It pairs a rapidly spinning white dwarf with a red dwarf companion in a tight orbit.
What makes AR Scorpii unique compared to other binary systems?
It holds the distinction of being the first confirmed white dwarf pulsar, meaning its compact companion exhibits pulsar-like behavior rather than the typical accretion-driven variability seen in other white dwarf binaries. This makes it a one-of-a-kind object in the catalog of multiple-star systems.
What are AR Scorpii's key timing parameters?
The two stars complete one orbit around their shared center of mass every 3.56 hours, while the white dwarf itself pulses on a much shorter 1.97-minute cycle. Its spin-down timescale of roughly ten million years gives researchers a window to study how such a system evolves over long timescales.
How did AR Scorpii get its variable-star designation?
Henrietta Swan Leavitt and Edward Charles Pickering first flagged the system as a variable star in 1904, and it formally received its variable designation in 1914. Early observers misread the 3.56-hour periodicity as a Delta Scuti-type pulsation before its true binary nature was understood.
Why do binary-star enthusiasts consider AR Scorpii important?
It provides the first real example of a white dwarf behaving as a pulsar, opening an entirely new category of compact-object behavior to study. Its relatively close distance of about 117 parsecs also makes it one of the more accessible targets for follow-up observations by both professional and amateur astronomers.
More in Binary and Multiple Stars, Part 3 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced