NASA’s new space telescope to scan extreme objects delivers its first image

It is called IXPE for Imaging X-ray Polarimetry Explorer. It’s a very small machine. One space telescope at X-rays say soft. Its objective: to study the radiation emitted by black holesmagnetars or neutron stars. In other words, the most mysterious objects in our Universe. And after being launched last December, it has just given its very first images.

For the first target, astronomers of the Nasa chose Cassiopée A, the remnant of a supernova located about 11,000 light years from our Earth. When the star at the origin of Cassiopeia A exploded in the XVII^and century, the shock waves heated the gas surrounding at very high temperatures and accelerated the cosmic particles. Result: a cloud 10 light-years in diameter that now shines in the X-ray range.

Much to expect from polarization

Cassiopeia A has already been the first object targeted by another space telescope to X-rays, Chandra. These images had revealed a compact object in the center of what was left of this supernova. Black hole or neutron star? The data returned by IXPE should make it possible to decide. In particular those relating to the polarization of X-rays, to the way in which this radiation is oriented when it travels in space. A polarization that holds clues to the environment in which these X-rays originated.

NASA astronomers are working on this first data to establish X-ray polarization maps from Cassiopeia A. “These images should reveal the mechanisms at the heart of this famous cosmic acceleratorexplains Roger Romani, a member of the team, in a communicated. Especially since theartificial intelligence and machine learning should make measurements even more accurate.”

IXPE, NASA’s new mission to explore black holes

In 2020, X-ray astronomy will have one more satellite to study it. IXPE, that’s its name, has just been selected by NASA. It will differ from other missions by an unprecedented ability to measure for the first time from space the polarization of X-rays emitted by the most extreme objects in the universe. Christian Gouiffès from the Serviceastrophysics at CEA-Saclay explains what it is all about.

Article of Remy Decourt published on 10/01/2017

Psyche and Lucy from the program Discovery, are not the only two missions selected by NASA at the start of the year. It also chose the IXPE mission (Imaging X-ray Polarimetry Explorer) as part of its Explorer program (13 other projects were in competition). IXPE aims to study for the first time hidden details of some of the most extreme astronomical objects and exotic of the universe, such as black holesneutron stars or pulsar. For this, he will measure the polarization of X-rays emitted by the superheated environment around these objects and will focus on the physics ofaccretion.

This satellite will be built by Ball Aerospace and will be equipped with polarization-sensitive X-ray detectors supplied by the Italian Space Agency. Costing approximately $188 million, IXPE will launch in 2020. It will succeed and join orbit a constellation of many other X satellites, proof of the interest of this wave length in observing the sky. So far, only balloons and sounding rockets had been used to observe this polarization in the cosmos.

Christian Gouiffès, from the Astrophysics Department at CEA-Saclay explains to us the characteristics of this mission which will open a new window on the universe and whose observations will not fail to amaze us.

How does IXPE differ from satellites operating in the X-ray domain?

Christian Gouiffes: This X-ray satellite differs from the X-ray satellites currently in operation (for example XMM-Newton of the’ESA Where Chandra NASA) essentially by the type of detector placed at the focal plane of telescopes. The latter responds to a scientific need which in the case of IXPE is the measurement of the polarization of celestial sources, a physical parameter which requires a particular experimental detection device. In all cases, the incident X-radiation is focused on a detection plane.

This satellite marks a technical breakthrough?

Christian Gouiffes: Yes, because so far detector types have been optimized for X-ray imaging and spectroscopy using X-ray sensitive CCDs (somewhat analogous to CCD cameras placed at homes optical telescopes). These increasingly efficient devices, successfully used by current X-ray space observatories, make it possible to provide images or maps of the sky in this field ofenergy X-rays, revealing the spatial structure of the celestial objects targeted or to decompose their X-light according to their energy (spectroscopy), a diagnostic providing information on the chemical nature of the environment (radiation-emitting elements). IXPE takes advantage of an innovative type of detector, invented and developed by Italian partner teams in the project, based on an imaging system sensitive to the polarization of incident light.

So this satellite combines two modes of observation?

Christian Gouiffes: Yes. By combining imaging capability and polarization measurement, the satellite will deliver important information on the properties and characteristics of the sources observed with unique instrumentation.

Is this where the originality of the project lies?

Christian Gouiffes: Yes, indeed, despite numerous attempts that have encountered various problems, including technological difficulties, practically no X space mission has had the detection of the X polarization of celestial sources at the heart of its program. However, the polarization of light is key information and an important parameter for better understanding the physics of objects (structure and amplitude of the magnetic field of the local environment, for example). This deficiency is somehow fixed with the acceptance of the IXPE project.

IXPE will open a new window on the universe?

Christian Gouiffes: Indeed. The development of high-performance detectors after years of study has just changed the panorama. Let us first mention, at the heart of these developments, the teams from Italian research laboratories, including that of Professor Enrico Costa (ASI/INAF). NASA’s acceptance of the IXPE project (equipped with Italian detectors) but also the pre-selection by ESA, the European Space Agency, of the XIPE mission (X-ray Imaging Polarimetry Explorer, M4 mission, launch in 2025) proves the maturity and originality of the project. These two missions have in common the detection plan, pixelated detectors sensitive to the polarization of X-ray light, coming from the Italian teams. This IXPE project will thus make it possible to complete the study of celestial X sources under a eye new, that of the analysis of polarized radiation. Structure and organization of the magnetic field at the heart of the targeted system are now within the reach of scientists. NASA’s IXPE and ESA’s XIPE missions complete and enrich the study of the sky in X-rays.

What is the main interest of observing the polarization in X?

Christian Gouiffes: The polarization of light gives access, whatever the wavelength studied, to information on the origin of the radiation and the nature of the medium in which it propagates. In the case of X-rays, very energetic radiation, it provides information on the medium located closest to the area ofepisode. Linked by nature to the electromagnetic component of radiation, polarization makes it possible to trace and/or trace the magnetic density content of the medium and its organization. To note just a few iconic high-energy objects, let’s mention the supernova remnantsthe close environment of active pulsars or on a larger scale, the active nuclei of galaxy.

What are the expectations of the community of astronomers working in this wavelength, in terms of scientific feedback or advances?

Christian Gouiffes: The main interest of this project lies in the fact that a dedicated X-ray space mission whose primary objective is polarization measurement is underway. The potential of studying the polarization of X-ray light from celestial sources sees in the acceptance of this NASA project, at the same time as the pre-selection of the ESA XIPE M4 mission, a major advance in a field which was not accessible except for the brightest objects.

Does the number and variety of detectable celestial sources therefore appear very promising?

Christian Gouiffes: Indeed yes. They open up interesting, unexplored avenues on the nature of X-ray emission phenomena at the heart of these systems through the analysis of a particular property of its light, its polarization.