Amazing discovery: Giant planet orbits tiny star

According to leading theories of planet formation, stars of this size should typically host small planets similar to Earth or Mars. However, the newly discovered planet is much larger.

Astronomers have discovered an unusual combination in the universe that has them baffled – an incredibly large planet orbiting an incredibly small star.

This discovery goes against current understanding of how planets form.

The star has only about one-fifth the mass of the Sun. According to leading theories of planet formation, stars of this size are usually only capable of hosting small planets similar to Earth or Mars.

However, the newly discovered planet is much larger – in fact, it is about the same size as Saturn, the second largest planet in the Solar System.

The star, called TOI-6894, is located about 240 light-years from Earth in the constellation Leo. (A light-year is the distance light travels in one year – 9.5 trillion kilometers).

It is the smallest star known to have a large planet orbiting it – about 40% smaller than the two previous records.

“The question this discovery raises is: How can such a small star have such a large planet – and we still don’t have the answer,” said astronomer Edward Bryant of the University of Warwick, lead author of the study published on June 4 in the journal Nature Astronomy.

Planets outside the Solar System are called exoplanets. The planet orbiting TOI-6894 is a gas giant, similar to Saturn and Jupiter in the Solar System, rather than a rocky planet like Earth.

The birth of a planetary system begins with a large cloud of dust and gas – called a molecular cloud – collapsing under the influence of gravity to form a central star.

The remaining material orbiting that star forms a protoplanetary disk, where planets form. Smaller clouds make smaller stars, and smaller disks have less material to form planets.

“It’s very difficult to form a giant planet in small clouds of dust and gas,” said study co-author Vincent Van Eylen, an exoplanet scientist at the Mullard Space Science Laboratory at University College London. “To do that, you need to quickly build a large planetary core and then rapidly accumulate a large amount of gas around that core. But the time frame for this is very short – before the star starts to brighten and the protoplanetary disk rapidly disappears. For small stars, we think there’s simply not enough material to build a large planet quickly enough before the disk disappears.”

No planet has ever been larger than its host star, and that's true in this case, but they're almost identical in size – a rarity.

While the Sun's diameter is 10 times larger than Jupiter (the largest planet in the Solar System), TOI-6894's diameter is only about 2.5 times larger than its planet.

This star is a red dwarf – the most common and smallest type of regular star, found throughout the Milky Way galaxy.
“Because these stars are so common, there may be more giant planets in our galaxy than we previously thought,” Bryant said.

The star TOI-6894 has about 21% the mass of the Sun and is much dimmer – the Sun's luminosity is about 250 times greater than it.

“This discovery shows that even the smallest stars in the universe can form very large planets,” added Van Eylen. “This forces us to reconsider some models of planet formation.”

The planet lies at a distance of just 1/40th that of Earth from the Sun, and completes one orbit in about three days. Given its close proximity, the planet has a fairly high temperature, though it is still not as hot as the “hot” gas giants, called “hot Jupiters,” that have been found orbiting larger stars.

The planet is slightly larger in diameter than Saturn and smaller than Jupiter, but is not as dense. Its mass is about 56% that of Saturn, and 17% that of Jupiter.

The main data used to study this planet was collected from NASA's Transiting Exoplanet Survey Satellite (TESS) and the European Southern Observatory's (ESO) Very Large Telescope (VLT) in Chile.

Researchers hope to better understand the planet's composition during observations scheduled next year with the James Webb Space Telescope.

“We predict that this planet has a large core, surrounded by a gaseous envelope of mostly hydrogen and helium,” Bryant said./.

(Vietnam News Agency/Vietnam+)

Source: https://www.vietnamplus.vn/phat-hien-kinh-ngac-hanh-tinh-khong-lo-quay-quanh-ngoi-sao-ti-hon-post1042479.vnp