ATHENA is an X-ray astrophysics observatory mission, which will provide a major advance in scientific capabilities compared with its predecessors (for example, XMM-Newton, Chandra, Suzaku, ASTRO-H).

This advance is required to address fundamental questions about the physical processes that shape the Universe.

ATHENA will impact astrophysics in the broadest sense, from the Solar System to stars, black holes and compact objects, supernovae and their remnants, galaxies, galaxy clusters, and large-scale cosmology.

While retaining the extremely broad scope of an observatory, ATHENA has been conceived to address the following specific science objectives:

• determine how matter accretes onto black holes and other compact objects, in environments where the strong gravity effects described by General Relativity apply;
  
  
• reveal the physics underpinning cosmic feedback and show how it relates the growth of supermassive black holes to the evolution of galaxies;
  
  
• trace the formation and evolution of large-scale structure via the properties of hot baryons in galaxy clusters and the cosmic web;
  
  
• determine the physical conditions in hot cosmic plasmas in all astrophysical environments, with fundamental impacts ranging from the Solar System to stars, galaxies and beyond.
  
  

Black holes, neutron stars and other compact objects

ATHENA will observe matter in the strong gravity regime within a few graviational radii of the event horizon of black holes. Large gravitational redshifts, extreme light bending and time-delay effects introduce distinctive spectral and timing signatures in the X-ray emission that will be readily measured by ATHENA.

The spin of astrophysical black holes will be measured by ATHENA through a variety of independent and complementary techniques.

ATHENA will enable multiple independent constraints to be obtained on the mass and radius of each neutron star observed, thus giving insights into the densest form of observable matter in the Universe and testing Quantum Chromodynamics.

Cosmic feedback

ATHENA will make a major contribution to the understanding of cosmic feedback - the process by which accretion and star formation are linked to the formation and evolution of galaxies - through the measurement of the volume-filling component of both the energy outflow from supermassive black holes and of the surrounding hot medium in galaxy bulges, groups and clusters.

Wide-area deep surveys with ATHENA will produce a census of the obscured growth of supermassive black holes in the Universe, which provide the power source driving feedback in the evolving galaxy population.

A survey of nearby AGN spins with ATHENA will probe in a unique way the growth modes of supermassive black holes (and galaxies) in the Universe.

Large-scale structure of the Universe

ATHENA's capability of performing spatially-resolved high-resolution spectroscopy will enable scientists to discern the fate of the hot baryons within the largest bound structures in the Universe. Motions, turbulence and thermal history of cluster gas will be measured through spatially resolved spectroscopy.

ATHENA has the unique capability to measure the abundances of all elements from Carbon to Zinc in the hot cluster gas, which reveals the supernova history and initial mass function of the parent stellar populations.

Cluster mass estimates out to z ~ 2 will be provided by ATHENA. From these, the dark energy density and equation of state out to that redshift can be derived. ATHENA will provide detailed parameters and astrophysical insight into clusters in the redshift range z ~ 1-2.

ATHENA will detect the Warm-Hot Intergalactic Medium both in absorption towards bright sources and in emission in filaments around clusters of galaxies, tracing regions where dark matter has accumulated.

Astrophysics of hot cosmic plasmas

ATHENA will also provide opportunities for major advances in the understanding of the nature and influences of hot cosmic plasmas in all classes of astrophysical objects. ATHENA will diagnose these hot cosmic plasmas via X-ray imaging and high-resolution X-ray spectroscopy.

In particular, ATHENA will:

• Measure the solar wind ionic composition and speed at varying distances and ecliptic latitudes via charge exchange X-ray emission in comets;
  
  
• Conclusively show the effects of X-ray stellar emission on exoplanets, as well as provide unique insights into the atmospheric evolution of habitable planets;
  
  
• Measure mass loss and magnetic fields in single and binary hot stars;
  
  
• Explore the variability of the accretion process and rotational modulation due to accretion stream shadowing in classical T-Tauri stars.
  
  
• Reveal the gas and dust chemical nature of the diffuse interstellar matter in the Galaxy;
  
  
• Determine the 3D structure of supernova remnants, thereby understanding shock properties and identifying the progenitor star.

(For more detailed information about  the science objectives of ATHENA, please consult the ATHENA assessment study report (Yellow Book) - see link in right-hand menu.)