Observing the Hot and Vibrant Universe-Sciencetimes

How can a black hole be observed?

Black holes are celestial bodies with strong gravity so that even light cannot escape. Compared to strong gravity, it is very small in size, and for this reason, it is almost impossible to directly observe a black hole. So how do we know the existence of a black hole?

Numerous dust and gases from the accretion disk around the black hole swirl and are slowly sucked into the black hole. Due to the friction that occurs at this time, the materials in the disk (ions and electrons) rise to a minimum absolute temperature of 10,000 degrees or more, and X-rays are emitted from the inside of the disk. Of course, according to recent research, it is expected that there will be many black holes that do not emit X-rays. However, high-energy X-ray emission is a phenomenon found only in very hot objects, which can be indirect evidence of a black hole.

Mankind’s strong aspiration to observe black holes

Since Earth’s atmosphere absorbs most of the X-rays from space, telescopes or probes for observing X-rays must go outside the Earth. The most successful X-ray project is the Chandra X-ray Observatory (also known as the Advanced X-ray Astrophysics Facility), which is a large strategic science program from NASA. It is one of the missions: or also known as Flagship missions), which is backed by a large budget. Through this, we can glimpse humanity’s strong desire to observe black holes.

A sophisticated and sensitive space telescope for observing high-energy celestial bodies was once again adopted by the European Space Agency (ESA). In 2014, the European Space Agency selected the Athena (Advanced Telescope for High Energy Astrophysics) project as the second large-scale L-class Cosmic Vision mission. Through the above mission, we plan to map the hot gas structures in the universe, study their physical properties, and observe supermassive black holes. As a result, they observe and study the hottest and most active universe.

The Athena Mission and the Scientific Objectives of the Mission

Athena was already named as the successor of XMM-Newton in the early 2000s, the XEUS program proposed by the European Space Agency, and the International X-ray Observatory (IXO), a combined program of Constellation-X proposed by NASA. It is a downgrade type of mission. In lieu of the IXO, which was canceled due to cost savings, a more economical Athena mission was once again proposed, which was finally selected by the European Space Agency and marked the start of the Athena mission. The Athena mission is a telescope that is at least 10 times more sensitive in many respects than its predecessors in X-ray exploration, such as the Chandra X-ray Observatory or XMM-Newton.

As can be seen in the subtitle of the Athena Mission, “The Hot and Vibrant Universe”, the scientific goals of the mission can be divided into two main categories. First, a mission is run aimed at answering a comprehensive and general question about how ordinary matter can make up the universe as we can see it today. Second, a black hole is a mission to answer questions about how it could grow and form the universe. Both questions can be answered by a sensitive X-ray observation mission. The Athena mission, which has significantly better condensing area, observation sensitivity, and observation speed than the full-time X-ray missions, can provide highly sensitive observations and research on various celestial bodies.

The Athena mission is expected to leave Earth with the Ariane 6.4 launch vehicle in the early 2030s and land at L2. The orbit around L2 was chosen on the basis of a stable thermal environment, good visibility and, most importantly, high observation efficiency, and is expected to perform up to 300 observations per year after normal settlement. The duration of the mission is at least 4 years, and it is a mission that can be extended afterwards. The telescope to be used for the Athena mission is a single telescope with a focal length of 12 m, and the effective area of ​​the telescope is approximately 1.4 square meters. The mirrors used in the telescope are directly manufactured based on the European Space Agency’s SPO (Silicon Pore Optics) technology, which provides excellent angular resolution and has an excellent collection area-to-mass ratio.

The two key machines to be mounted on the Athena mission, which passed all preliminary requirements specified by the European Space Agency in 2018 and 2019 respectively, are the Wide Field Imager (WFI) and the X-ray Integral Field Unit (X-IFU), respectively. WFI is a groundbreaking camera equipped with a spectrometer that boasts excellent energy resolution, low noise, and wide field of view of about 7 keV to 170 eV, based on Silicon DEPFET technology developed by the semiconductor laboratory of Max Planck Institute in Germany. The device is optimized for observing the sky with a wide field of view of about 40’x 40′ at a time, and includes a separate detector to find the brightest spots. WFI is being developed by Austria, Denmark, France, and Italy, centered on the Max Planck Extraterrestrial Astronomy Institute in Munich, Germany, a member of the European Space Agency. The X-IFU is a cryogenic X-ray spectrometer from the Athena Mission. The above equipment is a spectrometer with an optical resolution of up to 7 keV at 2.5 eV, and the X-IFU consortium consisting of Belgium, Czech Republic, Finland, France, Germany, Ireland, Italy, Netherlands, Poland, Spain, Switzerland, and Japan and the United States. It is developing with participation.

The appearance of the universe captured by X-rays is not surprising, so it is resilient. This is because X-rays emitted in the form of synchrotron radiation, brmsstrahlung radiation, and blackbody radiation are the hottest and most active celestial bodies in the universe. When the Athena mission is approved in the second half of 2022, including a final review by the European Space Agency, highly sensitive observation equipment will be used to provide detailed information on the high-energy phenomena of all celestial bodies, from the solar system to distant objects.

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