The Beacon: Hard Science Fiction by Brandon Morris (red white and royal blue hardcover TXT) 📕

expands. The resulting large redshift makes them challenging targets for an optical telescope, and an infrared telescope provides much more information.

In May 2008, an international group of infrared astronomers demonstrated that intergalactic dust greatly dims the light from distant galaxies. In reality, the galaxies are almost twice as bright as they look. The dust absorbs much of the visible light and emits it as infrared light.

To achieve a higher-angular resolution, infrared telescopes can be combined to form interferometers. As in the radio domain, the effective resolution of an interferometer is determined by the distance between the telescopes and not by the size of any of the individual telescopes. When combined with adaptive optics that compensate for the effects of the atmosphere, infrared interferometers can achieve particularly high angular resolution.

A special problem of infrared astronomy is that these telescopes require cooling. Infrared light is heat radiation. Every heat source is, therefore, a source of interference. Space telescopes are, in particular, continuously heated by the sun and must be extensively shielded and cooled. The low temperature is often achieved by using a coolant that will eventually run out. Several times, space missions have been either terminated or switched to observations in shorter wavelengths when coolant supplies were depleted. For example, the WISE space telescope ran out of coolant in October 2010, approximately ten months after launch.

Gravitational wave astronomy

Gravitational wave astronomy aims to use tiny distortions of space-time, as predicted by Albert Einstein’s general theory of relativity, to collect data on massive objects and any processes that trigger such distortions. These may include neutron stars and black holes, events such as supernovae, and the early universe shortly after the Big Bang.

Einstein first predicted the existence of gravitational waves in 1916. For a long time, however, researchers were unsure whether they actually existed or were just artifacts of the theory. Indirect evidence of their existence was first provided in the late 1980s by studying a binary system consisting of a neutron star and a pulsar, with the pulsar moving just as it would have to if gravitational wave emission were present. The discoverers, Hulse and Taylor, were awarded the Nobel Prize in Physics in 1993.

On February 11, 2016, it was announced that the LIGO collaboration had directly detected gravitational waves for the first time in September 2015. Barry Barish, Kip Thorne and Rainer Weiss were awarded the 2017 Nobel Prize in Physics for this achievement. LIGO works with two perpendicular arms over which laser pulses are sent. When a gravitational wave arrives, these arms are distorted differently. The travel time of the laser light changed minimally, which is visible through a changed interference pattern.

The fact that the measuring instruments have so far recorded mainly catastrophic events has a clear reason: The frequencies of ordinary gravitational waves are very low—their wavelengths are therefore very high. Thus they are much more difficult to detect by LIGO. Higher frequencies (shorter wavelengths) occur in more dramatic events. They distort the two arms of the measurement construction more strongly and could therefore be observed first. For the future, therefore, astronomers are looking to space-based detectors for which longer arms are possible. ESA, for example, is planning a gravitational wave mission to be launched in 2034 called the evolved Laser Interferometer Space Antenna (eLISA).

Another project is to measure pulsars precisely. If they are hit by gravitational waves, there should be transit time changes in their signals. Researchers worldwide are working together in so-called ‘pulsar timing arrays’ to track down gravitational waves of low frequencies. However, results are not expected for a few years.

Neutrino Astronomy

Neutrino astronomy observes astronomical objects with neutrino detectors. Neutrinos are produced during certain types of radioactive decay or nuclear reactions, such as those that occur in the sun, in nuclear reactors, or when cosmic rays strike atoms. Because of their weak interaction with matter, neutrinos offer a unique opportunity to observe processes inaccessible to optical telescopes.

Neutrinos continuously pass through the Earth in huge numbers. However, they interact so rarely with ordinary matter that only one interaction is registered per 1036 target atoms. And each interaction produces only a few photons or a single changed atom. Observation therefore requires a huge detector mass consisting of many atoms as well as a sensitive amplification system.

Given the very weak signal, sources of background noise must be reduced as much as possible. The detectors must be well shielded. Therefore, they are built deep underground or underwater. They detect particles flying upwards (i.e., coming from below them). ‘Upwards,’ because no other known particle can pass through the whole Earth, so that one is safe from interferences. The detectors must be located at a depth of at least one kilometer, and yet there is still an unavoidable background of extraterrestrial neutrinos interacting in the Earth’s atmosphere. The detectors consist of an array of light multiplier tubes housed in transparent pressure spheres, which in turn are suspended in a large volume of water or ice.

Why are neutrino detectors needed? If you look at celestial bodies like the sun in light of any wavelength, only the surface can be seen directly. Any light produced in the core of a star interacts with gas particles in the outer layers of the star and takes hundreds of thousands of years to reach the surface, making it impossible to observe the core directly. However, since neutrinos are also produced in the core of stars (as a result of nuclear fusion), the core is visible to neutrino astronomy.

Researchers have also discovered other sources of neutrinos, such as those released by supernovae. Several neutrino experiments have joined together to form the Supernova Early Warning System (SNEWS), looking for an increase in neutrino flux that could indicate a supernova event. Currently, astronomers are trying to detect neutrinos from other sources such as active galactic nuclei or gamma-ray bursts. Neutrino astronomy should also be able to indirectly detect dark matter.

So that you can also get something practical out of this, and perhaps give Peter a hand with his observations, I