Huge Alien Planet Forcing Host Star Age Prematurely

A nearby star is not acting its age, thanks to the influence of a massive exoplanet.

The close-orbiting alien planet, known as WASP-18b, is apparently disrupting the magnetic field of its host star so much that the object is behaving like a much older star, researchers said.

"WASP-18b is an extreme exoplanet," study lead author Ignazio Pillitteri, of the Instituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy, said in a statement.

"It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behaviour. The planet is causing its host star to act old before its time."

Artist's concept depicting the giant alien planet WASP-18b and its star, which are about 330 light-years away. 

Credit: NASA/CXC/M. Weiss

The star WASP-18, which lies about 330 light-years away, is about as massive as our own sun.

The gas giant WASP-18b weighs in at more than 10 times the mass of Jupiter and completes one orbit around the star in less than 23 hours, leading scientists to classify it as a "hot Jupiter."

WASP-18b's tight orbit has led scientists to estimate that it may have only one million years of life or so remaining before it's destroyed by the parent star.

Pillitteri's team targeted WASP-18 with NASA's Chandra X-ray Observatory and found it to be relatively quiet, a characteristic of older stars.

Young stars tend to be more active, with stronger magnetic fields, larger flares and more intense X-ray emission.

Stellar activity is connected to rotation, a process that slows with age.

Observations of WASP-18 using Chandra revealed no X-ray emission.

This by itself would suggest that the star has an age similar to the sun's 5 billion years, researchers said.

However, Pillitteri and his team used other data as well as theoretical models to calculate that WASP-18 is actually just 500 million to 2 billion years old, and thus approximately 100 times less active than a star its age should be.

"We think the planet is aging the star by wreaking havoc on its innards," said co-author Scott Wolk, of the Harvard-Smithsonian Center for Astrophysics (CfA) in Massachusetts.

WASP-18b's strong gravitational pull may be disrupting the star's magnetic field, researchers said.

The planet's tug exerts forces similar to those imposed on Earth's tides by the moon, but on a much larger scale.

SKA and CAASTRO: Forecast Sky bubbling with exploding stars

It is hard to imagine that any astronomical phenomenon could escape our latest and most powerful telescopes, but an international research team has now forecast some of the exotic discoveries that will only be able to be studied with the forthcoming Square Kilometre Array (SKA).

Giancarlo Ghirlanda

The team, led by Dr Giancarlo Ghirlanda at the National Institute for Astrophysics (INAF) in Italy and including CAASTRO members Dr Davide Burlon and Dr Tara Murphy from the University of Sydney, has calculated that the SKA will reveal the lingering footprints of tens of thousands of enigmatic cosmic explosions known as "gamma-ray bursts".

Davide Burlon

"With current telescopes, we see a bright gamma-ray burst somewhere in the Universe around once per day, but new radio telescopes will soon be able to see an afterglow of the explosion after the initial burst has faded away," explains CAASTRO postdoctoral researcher Dr Burlon.

"This afterglow can generally take weeks to gradually decay and teaches us incredible amounts about both the initial explosion and its neighbourhood."

The catch is that a gamma-ray burst is not an explosion that we can see from all directions but is comprised of a very narrow, energetic jet, so we need to be looking down the barrel of the jet at the right time.

Otherwise it is invisible, equivalent to only seeing the beam of a laser pointer when it points directly at us.

The radio afterglow should be visible from any direction though and for long periods of time, even if we missed the burst.

Tara Murphy

These afterglows without a burst are known as "orphan" afterglows, they're a phenomenon that astronomers have until now been looking for without success.

"From the rate at which we detect gamma-ray bursts, we were able to predict that with the power of a sensitive new telescope like the SKA, orphan afterglows should be seen 700 times more often than their gamma-ray bursts." says Dr Burlon.

"The unprecedented sensitivity and wide field-of view of the SKA means that orphan afterglows should be visible for months or even years before eventually disappearing, bubbling across the sky more than ten thousand times per year."

Of course, the SKA's view of the sky will be full of all sorts of objects and events, such as supernova explosions and flaring black holes that are more common than orphan afterglows.

"In this new era of radio astronomy, one of the challenges will be to disentangle these different classes of radio sources." says Dr Tara Murphy, CAASTRO Associate Investigator and project leader of the "Variables and Slow Transients (VAST)" survey with the Australian SKA Pathfinder (ASKAP).

The SKA will join the Australian SKA precursor telescope ASKAP and the South African SKA precursor MeerKAT in painting an entirely new picture of the "radio sky".

"The SKA will not only allow us to finally see these orphan afterglows but help us understand how gamma-ray bursts (GRB) produce such powerful, narrow jets and will cast new light on the big question of just what causes gamma-ray bursts in the first place," concludes Dr Ghirlanda.

More information: G. Ghirlanda, D. Burlon, G. Ghisellini, R. Salvaterra, M. G. Bernardini, S. Campana, S. Covino, P. D'Avanzo, V. D'Elia, A. Melandri, T. Murphy, L. Nava, S. D. Vergani, G. Tagliaferri: "GRB orphan afterglows in present and future radio transient surveys" in The Publications of the Astronomical Society of Australia (PASA). arXiv:1402.6338 [astro-ph.HE] arxiv.org/abs/1402.6338