Astronomers just saw a star eat a planet — an astrophysicist on the team explains the first-of-its-kind discovery


For the first time, astronomers have taken pictures showing a star devouring one of its planets. The star, called ZTF SLRN-2020, is located in the Milky Way, in the constellation Aquila. When the star swallowed its planet, the star brightened 100 times its normal level, allowing the 26-person team of astronomers I worked with to Detect the event as it happened.

I am a theoretical astrophysicistand developed computer models that our team uses to interpret the data we collect from telescopes. Although we only see the effects on the star, not the planet directly, our team is confident that the event we witnessed was a star swallowing its own planet. Witnessing such an event for the first time confirms the long-held assumption that it was being swallowed up by the stars planets He highlighted how this wonderful process was carried out.

Search for a twinkle in the dynamic night sky

My team researches the bursts of light and gas that occur when two stars merge into one larger star. To do this, we used data from Zwicky Transit Facility, a telescope located on Palomar Mountain in Southern California. They take nighttime pictures of large areas of the sky, and astronomers can then compare these images to find stars that change in brightness over time, called sidereal transits.

Finding stars that change in brightness isn’t the challenge – it’s sorting out the reason behind any particular change in a star. As my colleague Kechalay D He likes to say, “There are so many things that bloom in heaven.” The trick to identifying stellar mergers is to combine visible light – such as the data collected at Palomar – with infrared data from NASA’s WISE Space Telescopewhich has been scanning the entire sky for the past decade.

In 2020, the star ZTF SLRN-2020 suddenly became 100 times brighter visible light In just 10 days. Then it slowly started to fade back towards its normal brightness. About nine months ago, the same object began emitting a lot of infrared light, too. This is exactly what it looks like when two stars merge together, with one crucial difference – everything has been zoomed out. The overall brightness and energy of this event was about a thousand times lower than any of the merged star pairs astronomers have found so far.

When a star swallows its planets

Astronomers just saw a star eat a planet — an astrophysicist on the team explains the first-of-its-kind discovery

The star ZTF SLRN-2020 has increased in brightness in both the visible and infrared wavelengths of light, with the peak occurring on May 24, 2020. Credit: M. MacLeod, CC BY-ND

The idea that stars could swallow some of their planets was an old assumption in astronomy. Astronomers have long known that when the stars She ran out of hydrogen in her corethey get brighter and begin to do so increase in size.

Many planets have orbits smaller than the final size of the parent stars. Therefore, when the star runs out of fuel and begins to expand, the planets near it are inevitably consumed.

Interpretation of starbursts

In ZTF SLRN-2020’s outburst, our team never saw the planet itself, only brightening as the planet was absorbed by the star. This is where the combination is theoretical models with the monitoring data It allowed us to understand what the telescopes picked up.

The merger of two stars into one larger star is a Dramatic event that throw matter into the vicinity of stars. Much of my professional life has focused on Modeling the way stellar gases move And she bumps into herself and gets knocked out in these moments of intense interaction.

My work has shown that the total mass of matter ejected in a consolidation event is proportional to The size of the objects involved in the merger. Combine two equally large stars and you will see a huge disturbance. Merge one star with a much smaller companion and the event may eject a tiny fraction of the star’s total mass.

The energy released during ZTF SLRN-2020’s outburst was a thousand times less than normal for a two-star merger. This means that the object that merged with the star weighed a thousand times less than an ordinary star. This evidence pointed our team toward a gas giant – like Jupiter in our solar system, which weighs about a thousand times less than the sun.

The planet around ZTF SLRN-2020 skimmed the stellar surface before eventually falling into the star.

Compared to Jupiter, however, it should be for this planet orbiting near the starwith one revolution around the star taking only a few days. About 1% of the stars Share this formation of a large planet orbiting close to its parent star.

Furthermore, I believe that this formation of a large planet close to its star is important in generating the event that our team witnessed. My previous research suggests that smaller planets – or planets in more distant orbits that are consumed only after the star has grown significantly in size – might be Swallow without a detectable flash.

Learning from the real thing

With our data and the modeling of ZTF SLRN-2020, our team has been able to paint a much clearer picture of how stars and planets merge. First, the planet creeps across the surface of the star for many years, slowly heating up and expelling material from the atmosphere of the star. As this gas expands and cools, some particles and dust are formed. This cloud of dust gives the star a gradual red color and is emitting increasing amounts of infrared radiation.

In the case of ZTF SLRN-2020, the planet’s orbit contracted slowly at first, then faster and faster as the planet smashed through the denser layers of the star’s atmosphere. Eventually, within a few final days, the planet would fall below the star’s surface and be torn apart by the heat and force of the impact. This rapid injection of energy provided heat to increase the brightness of the ZTF SLRN-2020 for 10 days and hundreds of times. After this critical moment, the star began fading away, telling our team that the planet-swallowing process was over and the star began to return to business as usual.

While the devastating event has passed, there is still much to learn. Next week our team will start analyzing data from James Webb Space Telescope Hoping to learn about the chemistry of the gas that now surrounds ZTF SLRN-2020.

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