ESA Athena to study the hot and energetic universe

Artist's impression of an active galaxy. 

Credit: ESA/AOES Medialab

ESA has selected the Athena advanced telescope for high-energy astrophysics as its second 'Large-class' science mission.

The observatory will study the hot and energetic Universe and takes the 'L2' slot in ESA's Cosmic Vision 2015–25 plan, with a launch foreseen in 2028.

By combining a large X-ray telescope with state-of-the-art scientific instruments, Athena will address key questions in astrophysics, including: how and why does ordinary matter assemble into the galaxies and galactic clusters that we see today? How do black holes grow and influence their surroundings?

Scientists believe that black holes lurk at the centre of almost all galaxies and that they play a fundamental role in their formation and evolution.

To investigate this connection, Athena will observe X-ray emission from very hot material just before it is swallowed by a black hole, measuring distortions due to gravitational light-bending and time-delay effects in this extreme environment. Athena will also be able to determine the spin of the black hole itself.

Athena's powerful instruments will also allow unprecedented studies of a wide range of astronomical phenomena.

These include distant gamma-ray bursts, the hot gas found in the space around clusters of galaxies, the magnetic interplay between exoplanets and their parent stars, Jupiter's auroras and comets in our own Solar System.

"Athena will be a state-of-the-art observatory that will provide a significant leap forward in scientific capabilities compared with previous X-ray missions, and will address fundamental open questions in astrophysics," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"Its selection ensures that Europe's success in the field of X-ray astronomy is maintained far beyond the lifetime of our flagship observatory XMM-Newton."

The selection process for L2 began in March 2013, when ESA issued a call to the European science community to suggest the scientific themes to be pursued by the Cosmic Vision programme's second and third Large missions.

In November 2013, the theme of "the hot and energetic Universe" was selected for L2 for a launch in 2028, with "the gravitational Universe" selected for L3 and a planned launch in 2034.

Now officially selected for L2, Athena now moves into a study phase. Once the mission design and costing have been completed, it will eventually be proposed for 'adoption' in around 2019, before the start of construction.

After launch, Athena will travel to its operational orbit around the gravitationally semi-stable location in space some 1.5 million kilometres beyond Earth as seen from the Sun, a position coincidentally known as L2. ESA's Herschel, Planck and Gaia missions have also used L2 orbits.

The bow shock of Kappa Cassiopeiae, a massive, hot supergiant

The red arc in this infrared image from NASA's Spitzer Space Telescope is a giant shock wave, created by a speeding star known as Kappa Cassiopeiae. 

Credit: NASA /JPL-Caltech

Runaway stars can have a big impact on their surroundings as they plunge through the Milky Way galaxy.

Their high-speed encounters shock the galaxy, creating arcs, as seen in this newly released image from NASA's Spitzer Space Telescope.

In this case, the speedster star is known as Kappa Cassiopeiae, or HD 2905 to astronomers.

It is a massive, hot supergiant moving at around 2.5 million mph relative to its neighbors (1,100 kilometers per second) but what really makes the star stand out in this image is the surrounding, streaky red glow of material in its path.

Such structures are called bow shocks, and they can often be seen in front of the fastest, most massive stars in the galaxy.

Bow shocks form where the magnetic fields and wind of particles flowing off a star collide with the diffuse, and usually invisible, gas and dust that fill the space between stars.

How these shocks light up tells astronomers about the conditions around the star and in space.

Slow-moving stars like our sun have bow shocks that are nearly invisible at all wavelengths of light, but fast stars like Kappa Cassiopeiae create shocks that can be seen by Spitzer's infrared detectors.

Incredibly, this shock is created about 4 light-years ahead of Kappa Cassiopeiae, showing what a sizable impact this star has on its surroundings. (This is about the same distance that we are from Proxima Centauri, the nearest star beyond the sun.)

For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red.

The Kappa Cassiopeiae bow shock shows up as a vividly red colour. The faint green features in this image result from carbon molecules, called polycyclic aromatic hydrocarbons, in dust clouds along the line of sight that are illuminated by starlight.

Delicate red filaments run through this infrared nebula, crossing the bow shock. Some astronomers have suggested these filaments may be tracing out features of the magnetic field that runs throughout our galaxy.

Since magnetic fields are completely invisible themselves, we rely on chance encounters like this to reveal a little of their structure as they interact with the surrounding dust and gas.

Kappa Cassiopeiae is visible to the naked eye in the Cassiopeia constellation, but its bow shock only shows up in infrared light.