Giant ‘surviving’ planet found orbiting dead star | Space

Exoplanets have been found orbiting various types of stars, including some similar to our own sun and including red dwarf stars, the most common stars in our galaxy. But now, astronomers using data from NASA’s Transiting Exoplanet Reconnaissance Satellite (TESS) and the now retired Spitzer Space Telescope have announced something new: a Jupiter-sized planet orbiting a white dwarf star. White dwarfs are the small, very dense leftover cores of stars that were once similar to the sun and are now dead. If confirmed, this will be the first planet still intact to be found orbiting a white dwarf: a survivor of the dying of a star.

The peer-reviewed results were published in Nature on September 16, 2020. From the summary:

Here we report the observation of a giant planet candidate in transit by the white dwarf WD 1856 + 534 (TIC 267574918) every 1.4 days. We observe and model the periodic dimming of the white dwarf caused by the passage of the candidate planet in front of the star in its orbit. The candidate planet is roughly the same size as Jupiter and no more than 14 times as massive (with 95% confidence).

Finding a planet that still orbits a white dwarf is exciting because most planets that orbit a sun-like star would be destroyed when that star first expanded into a red giant star before shrinking to a remnant core. warm white. This planet, if further confirmed, survived that process.

The planet, named WD 1856 b, is about the size of Jupiter and orbits the white dwarf once every 34 hours. That’s 60 times faster than Mercury orbits the sun. This system is 80 light-years distant in the northern constellation Draco. The white dwarf is about 11,000 miles (18,000 kilometers) wide, can be up to 10 billion years old, and is a distant member of a triple star system.

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Normally, of course, we think that planets are much smaller than their stars. But in this case, the planet is orbiting a white dwarf, which is only 40% larger than Earth, so this planet is much larger than the white dwarf it orbits.

Andrew Vanderburg of the University of Wisconsin-Madison, who led the study, said in a statement:

WD 1856 b somehow got very close to its white dwarf and managed to stay in one piece. The process of creating the white dwarf destroys nearby planets, and anything that then gets too close is usually ripped apart by the star’s immense gravity. We still have many questions about how WD 1856 b got to its current location without encountering one of those destinations.

Co-author Siyi Xu, from the International Gemini Observatory in Hilo, Hawaii, said:

We have known for a long time that after the birth of white dwarfs, small distant objects, such as asteroids and comets, can scatter towards these stars. Usually the strong gravity of a white dwarf pulls them apart and they become a disk of debris. This is why I was so excited when Andrew told me about this system. We’ve seen hints that planets might also scatter inward, but this seems to be the first time we’ve seen a planet that made the entire journey intact.

Researchers aren’t sure how the planet managed to survive intact, but it may have been in a long, elliptical orbit. According to co-author Juliette Becker of Caltech:

The most likely case involves several other Jupiter-sized bodies close to the original orbit of WD 1856 b. The gravitational influence of such large objects could easily allow for the instability that you would need to push a planet inward. But at this point, we still have more theories than data points.

In a NOIRLab press release, Vanderburg commented on how surprising the discovery was, since only rocky debris had been seen around a white dwarf before:

The discovery was somewhat surprising. An earlier example of a similar system, where an object was seen passing in front of a white dwarf, showed only a field of debris from a disintegrating asteroid.

It’s also possible that the other two stars in the system, the red dwarfs G 229-20A and G 229-20B, exerted a gravitational pull on the planet for billions of years, with a subsequent flyby of a rogue star disrupting the system. .

The researchers used Spitzer to observe the system in infrared, just a few months before the space telescope was decommissioned and the mission ended. They concluded that the object was a planet and not a brown dwarf or low-mass star, as it did not emit any light on its own. When the researchers compared the Spitzer data with visible light transit observations taken with the Gran Telescopio Canarias in the Canary Islands, they saw no discernible difference. The age of the system and other data also told the researchers that the object was most likely a planet.

Vanderburg also commented:

Also, because we don’t detect any light from the planet itself, even in the infrared, it tells us that the planet is extremely cold, one of the coldest we’ve ever encountered.

Xu added:

We have had indirect evidence that planets exist around white dwarfs and it is amazing to finally find a planet like this.

As measured by Spitzer, the upper limit of the temperature on the planet is 63 degrees Fahrenheit (17 degrees Celsius), which is very similar to Earth. However, the planet is a gas giant, not a rocky world, so it is unlikely to be habitable in this case.

Follow-up observations were also made using the Hobby-Eberly 10-meter telescope at the McDonald Observatory at the University of Texas. Other observations included those from the Gemini Observatory, part of NOIRLab.

What’s next Could there be habitable planets around white dwarfs?

That answer may come with NASA’s upcoming James Webb Space Telescope (JWST). Vanderburg, along with co-author Lisa Kaltenegger and others, found that, using simulated observations, water and carbon dioxide could be detected in hypothetical rocky worlds orbiting white dwarfs by observing only five transits. These results are available in another article published in Astrophysical journal letters on September 16, 2020.

From the summary:

The short-term search for life beyond the solar system is currently focused on transiting planets orbiting small M dwarfs and the challenges of detecting signs of life in their atmospheres. However, planets orbiting white dwarfs (WD) would provide a unique opportunity to characterize rocky worlds … Rocky planets in the habitable zone of WD therefore represent a promising opportunity to characterize the atmospheres of the terrestrial planets and explore the possibility of a second genesis on these worlds.

Kaltenegger added:

Even more impressive, Webb was able to detect combinations of gases that could indicate biological activity in such a world in just 25 transits. WD 1856 b suggests that planets can survive the chaotic stories of white dwarfs. Under the right conditions, those worlds could sustain conditions favorable to life for longer than intended for Earth. We can now explore many new and intriguing possibilities for the worlds that orbit these dead stellar cores.

At Cornell Chronicle, Kaltenegger also said:

If rocky planets exist around white dwarfs, we could detect signs of life on them for years to come.

Co-lead author Ryan MacDonald expanded on this a bit, saying:

By observing Earth-like planets orbiting white dwarfs, the James Webb Space Telescope can detect water and carbon dioxide in a matter of hours. Two days of observation time with this powerful telescope would allow the discovery of gases with a biological signature, such as ozone and methane.

We now know that giant planets can exist around white dwarfs, and evidence dates back more than 100 years showing rocky material contaminating the light from white dwarfs. There are certainly small rocks in white dwarf systems. It is a logical leap to imagine a rocky planet like Earth orbiting a white dwarf.

It’s a pretty amazing thought, that life could still exist on a planet orbiting a star that’s long dead. As Kaltenegger reflected:

What if the death of the star is not the end of life? Could life go on, even after our sun has died? Signs of life on planets orbiting white dwarfs would show not only the incredible tenacity of life, but perhaps a glimpse into our future as well.

There are additional videos about this discovery on the Goddard Media Studios website.

Bottom line: for the first time, astronomers have detected a planet orbiting a white dwarf star.

Source: A candidate for a giant planet in transit by a white dwarf.

Source: The White Dwarf Opportunity: Solid Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope

Via NASA

Via NOIRLab

Via Cornell Chronicle