The author is an astronomer, science communicator and professor of science education at UQAM.
On May 12, astronomers from the Event Horizon Telescope (EHT) consortium unveiled the very first image of the gigantic black hole at the center of our galaxy, the Milky Way. With a mass four million times greater than that of the Sun, Sagittarius A* (that’s its name) is the second black hole of which we thus obtain a direct image, after the one that lands in the center of the giant elliptical galaxy M87, whose image was published by the same team in April 2019.
The EHT is a “virtual” telescope made up of eight radio telescopes scattered around the world. Each individual instrument observes the same target at the same time; the resulting images are then combined using powerful computers (called correlators) and ultra-precise atomic clocks. This makes it possible to produce a single image whose resolution, that is to say the ability to discern fine details, is equivalent to that of a single giant radio telescope whose diameter would be equal to that of the entire planet.
This is how the EHT made it possible to directly observe the black hole Sagittarius A*, an object whose diameter is smaller than that of Mercury’s orbit, but which is located more than 26,000 light years from Earth. This is a remarkable technological feat, the equivalent of observing a donut on the Moon.
Unfortunately, the future of this technology, like all radio astronomy research, is threatened by an insidious form of pollution which we hear little about, but which worries astronomers more and more: radio pollution. Terrestrial and space transmitters in the radio frequency domains useful in radio astronomy are indeed becoming more and more numerous and powerful, and literally “drown out” the weak signals coming from distant sources.
Radio frequencies are divided into blocks allocated to different users, in order to prevent interference between signals. For example, FM radio frequencies are in a separate block from AM radio, television, or police radio communications. The International Telecommunication Union, a UN agency, is responsible for managing these allocations, one of the purposes of the exercise being to protect the frequency bands that astronomers need to observe the sky. .
However, since the beginnings of the space era, the proliferation of satellites of all kinds (telecommunications, GPS, etc.) and the advent of mobile telephony, now ubiquitous, we are witnessing a slow erosion of the frequency bands assigned to radio astronomy and the encroachment by interference waves of certain frequency blocks reserved for research.
The situation is likely to get even worse with the proliferation of commercial companies willing to offer telephone and Internet services via satellite, such as SpaceX and OneWeb. Just for SpaceX, the company of Elon Musk, we are talking about eventually putting more than 35,000 satellites into orbit which will constantly exchange high-power radio signals with various terrestrial bases! For radio astronomers, it will be like trying to hear a whisper in the middle of a rock concert…
It is not only radio astronomy that is threatened: the proliferation of satellites in orbit around the Earth also creates a form of light pollution that will harm astronomical observation in the field of visible waves (light). During a virtual workshop held on March 25 under the aegis of the American Astronomical Society, astronomer Patrick Seitzer, of the University of Michigan, presented worrying figures: in a few years, more than 100 000 satellites which could thus clutter the low earth orbits.
It will then no longer be possible to observe distant stars and galaxies with the largest terrestrial telescopes without these spacecraft leaving a parasitic luminous trail on the astronomical detectors, ruining most of the observations.
Satellites are not the only threat to optical astronomy research. We already know the risks that light pollution poses to stargazing: by directly illuminating the sky, urban lighting creates a veil of light that prevents us from seeing the less brilliant stars. But now several energy producers are seriously studying the possibility of launching vast mirrors into orbit at an altitude of more than 800 km to reflect sunlight towards solar panel farms, which would allow the production of electricity to continue. even after sunset.
We can’t stop progress, but at what cost for astronomy? At the rate things are going, astronomers may soon have to go into exile on the dark side of the Moon to continue their exploration of the cosmos…