Chandra sees eclipsing planet in X-rays for first time

Jul 29, 2013
Using Chandra and XMM-Newton, astronomers have detected an exoplanet passing in front of its parent star for the first time in X-rays. The artist's illustration shows HD 189733b, a "hot Jupiter" that goes around its star once every 2.2 days. The illustration also reveals the presence of a faint red companion star in the system. The new X-ray observations (inset) suggest that HD 189733b has a larger atmosphere than implied by previous optical studies. HD 189733b is the closest hot Jupiter to Earth, making it a prime target for astronomers who want to learn more about this type of exoplanet and the atmosphere around it. Credit: X-ray: NASA/CXC/SAO/K.Poppenhaeger et al; Illustration: NASA/CXC/M.Weiss

For the first time since exoplanets, or planets around stars other than the sun, were discovered almost 20 years ago, X-ray observations have detected an exoplanet passing in front of its parent star.

An advantageous alignment of a planet and its in the system HD 189733, which is 63 light-years from Earth, enabled NASA's Chandra X-ray Observatory and the European Space Agency's XMM Newton Observatory to observe a dip in X-ray intensity as the planet transited the star.

"Thousands of have been seen to transit in only ," said Katja Poppenhaeger of Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led a new study to be published in the Aug. 10 edition of the Astrophysical Journal. "Finally being able to study one in X-rays is important because it reveals new information about the properties of an exoplanet."

The team used Chandra to observe six transits and data from XMM Newton observations of one.

The planet, known as HD 189733b, is a hot Jupiter, meaning it is similar in size to Jupiter in our solar system but in very close orbit around its star. HD 189733b is more than 30 times closer to its star than Earth is to the sun. It orbits the star once every 2.2 days.

HD 189733b is the closest hot Jupiter to Earth, which makes it a prime target for astronomers who want to learn more about this type of exoplanet and the atmosphere around it. They have used NASA's Kepler space telescope to study it at , and NASA's Hubble Space Telescope to confirm it is blue in color as a result of the preferential scattering of blue light by in its atmosphere.

The study with Chandra and XMM Newton has revealed clues to the size of the planet's atmosphere. The spacecraft saw light decreasing during the transits. The decrease in X-ray light was three times greater than the corresponding decrease in optical light.

"The X-ray data suggest there are extended layers of the planet's atmosphere that are transparent to optical light but opaque to X-rays," said co-author Jurgen Schmitt of Hamburger Sternwarte in Hamburg, Germany. "However, we need more data to confirm this idea."

The researchers also are learning about how the planet and the star can affect one another.

Astronomers have known for about a decade ultraviolet and X-ray radiation from the main star in HD 189733 are evaporating the atmosphere of HD 189733b over time. The authors estimate it is losing 100 million to 600 million kilograms of mass per second. HD 189733b's atmosphere appears to be thinning 25 percent to 65 percent faster than it would be if the planet's atmosphere were smaller.

"The extended atmosphere of this planet makes it a bigger target for high-energy radiation from its star, so more evaporation occurs," said co-author Scott Wolk, also of CfA.

The main star in HD 189733 also has a faint red companion, detected for the first time in X-rays with Chandra. The likely formed at the same time, but the main star appears to be 3 billion to 3 1/2 billion years younger than its companion star because it rotates faster, displays higher levels of magnetic activity and is about 30 times brighter in X-rays than its companion.

"This star is not acting its age, and having a big planet as a companion may be the explanation," said Poppenhaeger. "It's possible this hot Jupiter is keeping the star's rotation and magnetic activity high because of tidal forces, making it behave in some ways like a much younger star."

Explore further: Exoplanet measured with remarkable precision

More information: The paper is available online at: arxiv.org/abs/1306.2311

Related Stories

True colour of exoplanet measured for the first time

Jul 11, 2013

(Phys.org) —Astronomers using the NASA/ESA Hubble Space Telescope have, for the first time, determined the true colour of a planet orbiting another star. If seen up close this planet, known as HD 189733b, ...

Star blasts planet with X-rays

Sep 13, 2011

A nearby star is pummeling a companion planet with a barrage of X-rays a hundred thousand times more intense than the Earth receives from the Sun.

Astronomer uncovers the hidden identity of an exoplanet

Jul 01, 2013

(Phys.org) —Hovering about 70 light-years from Earth –– that's "next door" by astronomical standards –– is a star astronomers call HD 97658, which is almost bright enough to see with the naked eye. ...

Pulsating star sheds light on exoplanet

Jul 29, 2013

A team of researchers has devised a way to measure the internal properties of stars—a method that offers more accurate assessments of their orbiting planets.

Recommended for you

Exoplanet measured with remarkable precision

16 hours ago

Barely 30 years ago, the only planets astronomers had found were located right here in our own solar system. The Milky Way is chock-full of stars, millions of them similar to our own sun. Yet the tally ...

New star catalog reveals unexpected 'solar salad'

17 hours ago

(Phys.org) —An Arizona State University alumnus has devised the largest catalog ever produced for stellar compositions. Called the Hypatia Catalog, after one of the first female astronomers who lived in ...

New survey begins mapping nearby galaxies

Aug 18, 2014

A new survey called MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) has been launched that will greatly expand our understanding of galaxies, including the Milky Way, by charting the internal ...

User comments : 0