Incredible images show planets circling a star light-years away: ScienceAlert

A new video shared on YouTube is one of the most amazing things we’ve ever seen in planetary science.

The video shows four dots of light moving in partially concentric circles around a black disc in their center. What you’re actually looking at is a planetary system.

The four dots are exoplanets, with the black disk obscuring their star, 133.3 light-years away from Earth. The partial circles are their orbital motions, a time-lapse compiled from 12 years of observations.

The star is HR8799, and in 2008 his exoplanets formed the first system (not the first exoplanet, that was 2M1207b in 2004) that astronomers had once seen directly.

Since then, astronomer Jason Wang of Northwestern University has been watching closely. He compiled those observations into a time-lapse – not for any scientific reason, but just because it’s super cool.

“It’s usually hard to see planets in orbit,” says Wang.

“For example, that is not visible Jupiter or Mars revolve around our sun because we live in the same system and have no top view. Astronomical events happen too fast or too slow to capture in a movie.

“But this video shows planets moving on a human time scale. I hope it allows people to enjoy something wonderful.”

The current number of confirmed exoplanets – those are planets outside the solar system, or planets outside the solar system – numbers more than 5,200but most of them we have never seen.

Astronomers find exoplanets mainly through indirect methods, by studying the effect of the exoplanet on the host star. Regular, faint dips in the star’s light indicate an exoplanet orbiting between us and the star; faint changes in the wavelength of the star’s light indicate the gravitational interaction between exoplanet and star.

The reason for this is that it is actually extremely difficult to see an exoplanet directly. They are very small and very dim compared to their guest star; any light they emit or reflect is mostly swallowed up by the star’s bright light.

Occasionally, however, we get lucky. The exoplanets are large and sufficiently distant from their star, and the system is oriented so that, if the star’s light is blocked or obscured (which is why HR8799 appears as a black disk), we can see them as little blobs of associated light.

Even rarer is to see them perform their complex planetary pavane, simply because the timescales of the orbits involved are much longer than the time since scientists directly saw the first exoplanet.

But Wang and his team now have enough observational data from HR8799 for a time-lapse showing partial orbits, which is what he gathered.

“There’s nothing to be scientifically gained by looking at the orbital galaxies in a time-lapse video, but it helps others appreciate what we’re studying,” says Wang.

“It can be difficult to explain the nuances of science with words. But showing science in action helps others understand its importance.”

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The observations were collected using the WM Keck Observatory and Wang applied adaptive optics to correct for the distorting effect of Earth’s atmosphere.

The time-lapse has also been processed to correct for the temporal jumps between data, showing the smooth orbital motion of the four exoplanets.

The 12-year observation has sped up to just 4.5 seconds.

Here’s what you’re looking at. The black circle in the center is the young 30-million-year-old star, about 1.5 times the mass and 4.9 times the luminosity of the Sun.

The innermost exoplanet is HR8799e, with a mass of 7.4 Jupiters orbiting at a distance of 16.25 times the distance between Earth and the Sun, or astronomical units, over an orbital period of 45 years. Scientists have been able to analyze the light from this exoplanet to determine that it is a stormy baby gas giant.

Moving outward, HR8799d has the mass of 9.1 Jupiters, and orbits 26.67 astronomical units over a 100-year orbital period.

HR8799c is 7.8 Jupiters in mass, orbiting at a distance of 41.4 astronomical units (just slightly wider than the distance between the Sun and Pluto) during an orbital period of 190 years. It has water in its atmosphere, scientists have found.

Finally, HR8799b clocks in at 5.7 Jupiters, with a separation of 71.6 astronomical units and an orbital period of 460 years.

But we are far from done with the HR8799 system.

While the time-lapse itself may not be scientifically revealing, according to Wang, the Keck data set certainly is.

A paper published in December last year found the possible existence of a fifth exoplanet, smaller and closer to the star than its siblings. The candidate is estimated to be about 4 to 7 times the mass of Jupiter, orbiting between 4 and 5 astronomical units away, making it more difficult to spot directly.

And Wang and his colleagues are hard at work analyzing the system’s light. They hope they can get detailed information about the composition of not only the star, but also the world around it.

“In astrophysics, we’re usually doing data analysis or testing hypotheses,” says Wang.

“But this is the fun part of science. It inspires awe.”