Gemini Planet Imager (GPI): New imaging technique reveal planets near bright stars

The GPI is mounted on mounted on a side port of the instrument support structure of the Gemini South telescope. 

Credit: Gemini Planet Observatory

The Gemini Planet Imager (GPI) was built for one purpose: imaging extrasolar planets.

In the seven months since it came online, GPI is proving to be an order-of-magnitude improvement-so much so that it may rewrite the rules of planet-hunting.

Planet-hunting bears some similarity to tracking a rare species through the jungle.

There are a variety of ways to know that it's there, most of which are indirect: The leaves rustling. The undergrowth is trampled. The animal's shadow appears for a fleeting moment before it fades away again.

It is much the same with planets. We can detect them moving their parent planets ever-so-slightly via Doppler shift.

GPI functioning testbed system

We can see the light from that star dim as an exoplanet-or the planet's shadow-passes in front of it.

Once in a while, a young star's dust disk will have a gap in it, from which we infer the presence of a formed or forming planet.

These detection methods have allowed us to catalog over 1700 exoplanets since 1994.

Naturally, ultimate achievement in observation is to see the species or the planet with our own eyes.

That's what the Gemini Planet Imager (GPI) does best: direct detection of exoplanets.

Technically, direct detection means spatially resolving the light of a planet from the light of its parent star: taking a picture of the planet itself.

Before GPI, there were serious limitations to our ability to photograph an exoplanet.

Optical design of the GPI science camera.

The photographic exposure had to be long and the contrast between the star and the exoplanet had to be high. With GPI, what used to be a one-hour photo has become a one-minute photo.

The contrast can be three orders of magnitude lower - the planet can be 1000 times dimmer - and the photo will still turn out.

Micro-Electro-Mechanical Systems (MEMS) mirrors

This remarkable improvement in exoplanet imaging is achieved with a variety of new technologies: for example, deformable silicon Micro-Electro-Mechanical Systems (MEMS) mirrors.

The mirrors can bend and flex in ways that counters atmospheric distortion.

GPI also has a diffraction-suppressing coronagraph, which blocks the light from the parent star so that the planet can be seen more clearly, and an integral field spectrograph, which allows spectra to be taken over an entire two-dimensional field of the sky.

By combining these and other related technologies, images like the now-famous photo of Beta Pictoris b are produced.

They reveal planets many dozens of light years away glowing with residual radiation from their formations millions of years ago.

The bright white dot is the planet Beta Pictoris b, glowing in the infrared light from the heat released when it was formed 10 million years ago. 

The bright star Beta Pictoris b is hidden behind a mask at the center of the image. 

Credit: GPI

GPI can also supply information about the exoplanet's atmospheric composition and interactions with nearby objects such as asteroid belts.

GPI was deployed on the 8-m Gemini South telescope in Chile. Its first image or "first light" took place in November 2013.

Since then, GPI has done an unprecedented job of capturing Jupiter-sized objects around stars similar to our Sun. 

Green Bank Telescope: Hidden details revealed in nearby starburst galaxy

This composite image of starburst galaxy M82 shows the distribution of dense molecular gas as seen by the GBT (yellow and red) and the background stars and dust as seen by the Hubble Space telescope (blue).

The yellow areas correspond to regions of intense star formation.

The red areas trace outflows of gas from the disk of the galaxy. 

Credit: Bill Saxton (NRAO/AUI/NSF); Hubble/NASA

Using the new, high-frequency capabilities of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomers have captured never-before-seen details of the nearby starburst galaxy M82.

These new data highlight streamers of material fleeing the disk of the galaxy as well as concentrations of dense molecular gas surrounding pockets of intense star formation.

M82, which is located approximately 12 million light-years away in the constellation Ursa Major, is a classic example of a starburst galaxy—one that is producing new stars tens- to hundreds-of-times faster than our own Milky Way.

Its relatively nearby location made it an ideal target for the GBT's newly equipped "W-Band" receiver, which is capable of detecting the millimeter wavelength light that is emitted by molecular gas.

This new capability makes the GBT the world's largest single-dish, millimeter-wave telescope.

Amanda Kepley

"With this new vision, we were able to look at M82 to explore how the distribution of molecular gas in the galaxy corresponded to areas of intense star formation," said Amanda Kepley, a post-doctoral fellow at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and lead author on a paper accepted for publication in the Astrophysical Journal Letters.

"Having this new capability may help us understand why stars form where they do."

Astronomers recognize that dense molecular gas goes hand-in-hand with areas of star formation, but the connection is poorly understood and this relationship may be different in different types of galaxies.

By creating wide-angle maps of the gas in galaxies, astronomers hope to better understand this complex interplay.

To date, however, these kinds of observations have not been easy since molecules that are used to map the distribution of dense gas, like HCN (hydrogen cyanide) and HCO+ (formylium), shine feebly in millimeter light.

With its new W-Band receiver, the GBT was able to make highly sensitive, wide-angle images of these gases in and around M82.

"The GBT data clearly show billowing concentrations of dense molecular gas huddled around areas that are undergoing bursts of intense star formation," said Kepley.

"They also reveal giant outflows of ionized gas fleeing the disk of the galaxy. These outflows are driven by star formation deep within the galaxy."

This capability will enable astronomers to quickly survey entire galaxies and different parts within galaxies.

Such surveys would complement higher resolution observations with new Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.

The 100-meter GBT is located in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone, which protect the incredibly sensitive telescope from unwanted radio interference.

ESA Hubble Image: Sparkling Hook, a nearby starburst galaxy

Credit: ESA Hubble

Visible as a small, sparkling hook in the dark sky, this beautiful object is known as J082354.96 for short.

It is a starburst galaxy, so named because of the incredibly (and unusually) high rate of star formation occurring within it.

One way in which astronomers probe the nature and structure of galaxies like this is by observing the behaviour of their dust and gas components; in particular, the Lyman-alpha emission.

This occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so.

This emission is interesting because this light leaves its host galaxy only after extensive scattering in the nearby gas—meaning that this light can be used as a pretty direct probe of what a galaxy is made up of.

The study of this Lyman-alpha emission is common in very distant galaxies, but now a study named LARS (Lyman Alpha Reference Sample) is investigating the same effect in galaxies that are closer by. The study is published in Astrophysical Journal Letters.

Astronomers chose fourteen galaxies, including this one, and used spectroscopy and imaging to see what was happening within them.

They found that these Lyman-alpha photons can travel much further if a galaxy has less dust—meaning that we can use this emission to infer how dusty the source galaxy is likely to be.