This planetary nebula has 2 ultra-close stars at its heart
EarthSky in SPACE | October 24, 2018
A planetary nebula isn’t related to planets. It’s an old star, sloughing off its outer layers. Now astronomers have spied 2 ultra-close stars at a planetary nebula’s heart. The pair orbits in only 3 hours!
The Hubble Space Telescope captured this image of the planetary nebula M3-1. Its central star is a binary system – 2 stars orbiting a
common center of gravity – extremely close together, moving around each other very fast. Image via David Jones/Daniel López (IAC)/RAS.
EarthSky in SPACE | October 24, 2018
A planetary nebula isn’t related to planets. It’s an old star, sloughing off its outer layers. Now astronomers have spied 2 ultra-close stars at a planetary nebula’s heart. The pair orbits in only 3 hours!
The Hubble Space Telescope captured this image of the planetary nebula M3-1. Its central star is a binary system – 2 stars orbiting a
common center of gravity – extremely close together, moving around each other very fast. Image via David Jones/Daniel López (IAC)/RAS.
An international team of astronomers have discovered two stars in a binary pair that complete an orbit around each other in a little over three hours, residing in the planetary nebula M3-1. Remarkably, the stars could drive a nova explosion, an entirely unexpected event based on our current understanding of binary star evolution. The team, led by David Jones of the Instituto de Astrofísica de Canarias and the Universidad de La Laguna, report their findings in Monthly Notices of the Royal Astronomical Society: Letters.
Planetary nebulae are the glowing shells of gas and dust formed from the outer layers of stars like our own sun, which they throw off during the final stages of their evolution. In many cases, interaction with a nearby companion star plays an important role in the ejection of this material and the formation of the elaborate structures seen in the resulting planetary nebulae.
The planetary nebula M3-1 is located in the constellation of Canis Major, at a distance of roughly 14,000 light-years from Earth. M3-1 was a firm candidate to host a binary central star, as its structure with prominent jets and filaments is typical of these binary star interactions.
Using the telescopes of the European Southern Observatory (ESO) in Chile, Jones’s team looked at M3-1 over a period of several years. In the process they discovered and studied the binary stars in the centre of the nebula. Brent Miszalski, researcher at the Southern African Large Telescope, and co-author of the study, commented:
We knew M3-1 had to host a binary star, so we set about acquiring the observations required to prove this and to relate the properties of the nebula with the evolution of the star or stars that formed it.
The two stars are so close together that they cannot be resolved from the ground, so instead the presence of the second star is inferred from the variation of their observed combined brightness – most obviously by periodic eclipses of one star by the other which produce marked drops in the brightness. Henri Boffin, researcher at the European Southern Observatory in Germany, said:
When we began the observations, it was immediately clear that the system was a binary. We saw that the apparently single star at the center of the nebula was rapidly changing in brightness, and we knew that this must be due to the presence of a companion star.
The team discovered that the central star of the planetary nebula M3-1 has one of the shortest orbital period binary central stars known to date, at just over three hours. The ESO observations also show that the two stars – most likely a white dwarf with a low-mass main sequence companion – are almost touching.
As a result, the pair are likely to undergo a so-called nova eruption, the result of the transfer of material from one star to the other. When this reaches a critical mass, a violent thermonuclear explosion takes place and the system temporarily increases in brightness by up to a million times.
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