Most of the exoplanets we’ve confirmed to date have never really looked straight. We confirm their presence through indirect means, such as their effect on their host star. But now, astronomers have released images of exoplanets found indirectly.
It is not just an impressive feat of skill and technique. The combination of methods has given us a cool toolkit for measuring exoplanets. For the first time, astronomers have measured both brightness and mass of exoplanets – a new probe into how planets form.
The exoplanet is Beta Pictoris C (β PCC), the gas giant orbiting the star – you guessed it – Beta Pictoris, just 63 light-years away. It is a very young, very bright star, about 23 million years old; As such, it is still surrounded by lots of dusty debris, and its exoplanets – we have confirmed two dates – are just babies, about 18.5 million years old.
β PCA is the second of the planets, and it was found using the radial velocity method. The stars, you see, do not sit still when the planets revolve around it; Both bodies attach a gravitational tug to each other, and the orbits revolve around the mutual center of gravity.
So, if you look at a star and you see it wandering around a bit – its light gets longer in wavelength or redshafting, as it moves forward, and shorter in blur length or blueshifting, as it gets closer. Goes, often means that it is tugged by the exoplanet. The larger the exoplanet, the larger the gravitational tug it spreads over the star.
Beta Pictoris B (β Peak B), a gas giant up to 13 times the mass of Jupiter, was discovered in 2008 by direct imaging. Therefore, it was expected that the star would sink.
But, while studying observational data taken over the previous 16 years, astronomer Anne-Marie Lagrange of the French Grenoble Observatory and colleagues noted that a was inconsistent with Peak B. Instead, it seemed to be another, previously undiscovered exoplanet.
They unveiled their newly discovered Exoplanet – C Peak Sea – last year.
Enter the Exogravity Collaboration, project using the Gravity Instrument for straight image explanites on a fairly large telescope interferometer. The Exogravity team thought β PC would be an excellent candidate for direct imaging.
They were looking for an exoplanet with a good set of radial velocity data and the Peak Sea siblings were already directly imaged, so it felt like a good bet.
Very few exoplanets can be directly imaged with our current technology. They need to be far enough away from their star; Otherwise they disappear into glare. Our most reliable exoplanet detection methods work best on very close stars. And it is helpful if the exoplanet is quite young, because such planets are still warm enough to emit thermal radiation.
As it turned out, β Pic c was perfect. Those years of sunken data provided an excellent outline of the movement of the exoplanet; The Exogravity team, led by Cambridge University astronomer Matthias Navak in the UK, was able to get to the location and get direct images. That work now picks up the Exoplanet dataset we never had before.
Radial velocity data were used to calculate the mass and orbit of the exoplanet; It is about 8.2 times the mass of Jupiter’s mass, and orbits the star in 2.7 astronomical units, with an orbital period of 3..4 years. So far, so normal.
But the straight images revealed a surprise – β PC is surprisingly stupid, six times stupid than its siblings, even though the two exoplanets are the same size, indicating that it is too cold. The brightness of β PC indicates that its temperature is around 1,250 Kelvin, compared to 1,724 Kelvin for બી Peak B.
This may be the key to how the exoplanet is formed: in the models, the temperature of the baby’s exoplanet is related to the method of its formation.
In the disk instability formation model, part of the dust and gas protoplanetary disk revolving around the newborn star falls directly into the gas giant. In this model, the exoplanet has no solid core, and that makes it warm and bright.
In the main attraction model, pieces of rock stick together in a protoplanetary disk, first by electrostatic forces, then by gravity, forming larger and larger bodies, forming planets from below. The resulting exoplanet has a solid core, and forms a cooler and dimmer.
Because the β PC is smaller and more obscure than expected, and because the disk instability model requires an exoplanet to form further away from its host star than the host PC, the team believes that the exoplanet created by major growth.
That’s a lovely result, but there’s still work to be done. We don’t have a reliable mass estimate for Peak B – it could be anywhere between 9 and 13 times Jupiter’s mass. It orbits a star at a distance greater than 5 PCC, which means that we do not have enough sunken data to estimate its mass. It will be difficult to gauge how we formed it until we can reduce it.
And β Pic c. More work to be done. The next step is to take a detailed spectra of the light emitted by the exoplanet. Of these, scientists could work on the planet’s atmospheric composition – a major technique for finding signs of life elsewhere in the galaxy.
The research is published in two papers Astronomy and astrophysics, Here and here.
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