The distant future solar system is safe from a collision with a runaway dead star.
Last year, researchers examined the trajectory of a white dwarf star called WD 0810-353 with the Gaia space telescope and predicted that it would encounter our solar system in about 29,000 years. Although this may seem like a long time in human terms, it is a relatively short period of time from a cosmic perspective. For example, the Sun will not run out of hydrogen and become a red giant for another 5 billion years, destroying Earth and the inner planets.
Although the Sun’s fate is likely sealed, new research has revealed that our planet, at least, need not fear being decimated by the chaos caused by the runaway white dwarf WD 0810-353. In fact, the “rogue” star won’t just miss the solar system; it might even not be our direction at all, say astronomers.
“We found that the approach speed measured by the Gaia project is incorrect and that the predicted close encounter between WD0810-353 and the sun will not occur,” astronomer Stefano Bagnulo said in a statement. “In fact, WD0810-353 may not even be heading toward the sun at all. That’s one less cosmic danger we have to worry about!”
What did Gaia do wrong?
Gaia is a space telescope currently building an extraordinarily precise three-dimensional map of more than a billion stars throughout our galaxy, the Milky Way. It does this by precisely measuring the positions of stars and tracking changes in those positions by returning that “slice” of the sky and observing it again to see what has changed.
In 2022, astronomers Vadim Bobylev and Anisa Bajkova analyzed the vast Gaia dataset, looking for stars that appear to be heading toward the solar system. This led them to WD 0810-353, a white dwarf star – a type of dense stellar remnant left when stars of similar mass to the sun die.
Our own sun will become a white dwarf about a billion years after its destructive spell as a red giant, when the sun’s bloated outer layers cool and recede, leaving behind a smoldering core.
WD 0810-353 could offer a glimpse of what the sun will look like at that time when it is about half a light year from the solar system, or about 31,000 times the distance between Earth and the sun .
Although this seems anything but a close encounter, it is close enough that the gravitational influence of WD 0810-353 could disrupt the Oort Cloud – a body of comets and other icy bodies at the edge of the solar system.
The Oort Cloud is located between 2,000 and 100,000 times the distance between Earth and the sun from the central star of the solar system. When the cloud is displaced by passing stars like WD 0810-353, the star’s gravity could send some of these weakly gravitationally bound icy bodies plummeting toward the inner solar system and Earth.
So what happened with the sightings of this rogue white dwarf? What made astronomers think it was headed our way, and how do we know it probably isn’t?
A magnetic confusion
While making her observations of WD 0810-353, it turns out that Gia missed something important and unusual about this white dwarf. It has a strangely large magnetic field.
“Unusually, this old white dwarf also has a huge magnetic field,” says Eva Villaver, an astronomer at the Center for Astrobiology in Spain and co-author of the study. “In astronomy, magnetic fields are essential to understanding many physical aspects of a star, and failing to take them into account can lead to misinterpretations of physical phenomena.”
Astronomers had determined that WD 0810-353 was moving toward us by calculating the white dwarf’s radial velocity — the speed of an object along the observer’s line of sight to that object. This is done by examining the spectrum of light emitted by the star and then dividing it into the constituent wavelengths that make up that light.
If a star moves away from us, it stretches the wavelengths, causing light to shift toward the red end of the electromagnetic spectrum, a phenomenon known as redshift. However, if a star moves toward us, the wavelength of the light it emits is compressed and shifts toward the blue end and is described as being “blue-shifted.”
The fact is that magnetic fields can also affect the spectrum of light from a star, dead or not, by splitting the spectral lines and shifting them to other wavelengths.
To determine whether this was the case with WD 0810-353, Bagnulo turned to the Very Large Telescope (VLT) located in northern Chile, and in particular to an instrument called FOcal Reducer and Low Dispersion Spectrograph 2 (FORS2 ).
FORS2 allowed the team to obtain a very precise image of the spectra of WD 0810-353 and to see if its intense magnetic field was disturbing Gaia. This is possible because light waves generally oscillate in all directions, but when introduced into a magnetic field, they begin to oscillate in a preferred direction, thus becoming “polarized.”
Using polarized light from this white dwarf, the team modeled the dead star’s magnetic field and found that its trajectory and speed could actually be the result of a strong magnetic field. This means the solar system is likely safe from this rogue white dwarf.
The team’s research is published in the Astrophysical Journal.
Originally published on Espace.com.