Stars’ twinkle

HIGH PERCENTAGE OF STARS HAVE EATEN A PLANET, RESEARCH FINDS

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DON’T UNDERESTIMATE THEIR APPETITE.

Deadly Diet

New research has shown that about one in 12 stars have devoured a planet, suggesting that stable planetary systems like our own are less common throughout the cosmos than once believed.

As detailed in the study, published in the journal Nature, the researchers analyzed the chemical composition of nearby stars to search for signs that they’d ingested planetary material.

Limiting their focus to binary stars, they found that at least 8 percent of these stellar pairings — seven out of 91 in total — showed chemical signs of planetary ingestion, or “planet signatures.”

“What’s truly surprising is the frequency at which it seems to happen,” study co-author Yuan-Seng Ting, an astronomer at the Australian National University, told Space.com. “It implies that stable planetary systems like our own solar system might not be the norm. This gives us a deeper perspective on our place in the universe.”

Profitable Pairings

Using data from a census of binary systems, the researchers focused on stars that were born together.

These so-called “co-natal” stars are effectively identical twins, meaning that when one of them undergoes a change in chemical composition, it’s much easier to notice. This also helps rule out other potential causes, ensuring as much as possible that what the readings are seeing are indeed planet signatures and not something else.

“We found that some stars differed from their twins,” the authors explained in a writeup for The Conversation, “showing a distinct chemical pattern with higher amounts of certain elements like iron, nickel and titanium compared to others such as carbon and oxygen.”

“These differences indicate strong evidence that the star has ingested a planet,” they added.

Unsure Footing

The reason so many planets are falling into their stars, the researchers suggest, is due to them developing a “wobble.”

Such instability can often arise in systems that have three or more significantly large moving bodies — read: the three body problem — because they gravitationally interact in extremely complex ways in which even the most subtle perturbations, when played out over millions of years, can destabilize the whole cosmic dance.

That’s why stars and planets can get ejected from their systems, or in this case get wholly devoured. As to whether that means our own planet will get cannibalized by the Sun this way, the researchers say it’s not likely.

“Our study does not suggest we are likely to see such instabilities in our own Solar System,” they wrote in The Conversation. “Even with our new results, however, it is important to recognize that planet engulfment and instability still occur only in a minority of cases.”

Stars’ twinkle reveals their character.

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In 1806, English poet Jane Taylor famously lamented that a little star’s twinkle left her wondering what it was.

Fast-forward 207 years and a new analysis of starlight collected by NASA’s Kepler space telescope shows patterns in the flicker that are directly tied to the amount of boiling taking place on a star’s surface, a key indicator of its size, mass and evolutionary state.

That information, in turn, reveals volumes about any orbiting planets, including those fortuitously positioned from their parent stars for liquid surface water, apparently a key ingredient for life.

“Everything you know about planets is tied to what you know about the host star,” says Fabienne Bastien, an astronomy graduate student at Vanderbilt University.

“We don’t observe the planets directly. We observe the stars and the influence that the planets have on their stars. So in order to make any conclusions about the size of the planet or the mass of the planet as it’s pulling on the star when it’s moving, you need to know the size and the mass of the star very well.”

“That directly impacts whether or not you can claim that you have an Earth-like planet,” she says.

Bastien, who is working on a doctoral dissertation, was analysing archived Kepler data for a totally different reason when she and colleagues chanced upon strange patterns in the data that they didn’t understand.

“It was a complete surprise,” says Bastien.

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Boiling surfaces

It turns out the pattern provides a quick and relatively reliable way to determine a star’s evolutionary state.

Stars like the Sun, which is about 4.6 billion years old, eventually will evolve into red giants as they run out of fuel for nuclear fusion. The new study shows the surfaces of younger dwarf stars boiling more vigorously than older giants.

“What we are looking at here is the gravitational acceleration in the stellar outer layers, what we often call the atmosphere,” says astronomer Joergen Christensen-Dalsgaard, with Aarhus University in Denmark.

“The typical methods used have uncertainties up to 150 per cent. That very imprecise method is the easiest to do, and especially if you’re dealing with 150,000 stars and you need to characterise them all, that’s what you go to because it takes the least amount of resources. Our technique lets us beat that down to 25 per cent, which is very, very good for this field,” added Bastien.

Kepler, which collected data from about 120,000 target stars between May 2009 and May 2013, was designed to search for Earth-like planets in stars’ habitable zones,

For Bastien’s study, which appears in this week’s edition of Nature, astronomers analysed a few thousand stars in the Kepler data archive.

“If you have a large enough sample, then you start to pick out patterns in the way stars of different evolutionary states behave,” she says.

While the study is based on eight-hour flicker patterns in the visible light coming from target stars, scientists translated the data into corresponding audio wavelengths, a poignant conceptualisation that no doubt would have intrigued, and delighted, poet Taylor.

Source: http://www.abc.net.au