Cosmic Drama

Gamma-ray bursts are caused by gigantic explosions in the depths of space. Astrophysicists from the University of Tübingen have developed the technology on board a nanosatellite that is being dispatched to precisely locate them.

Gamma-ray bursts are among the most cataclysmic events in the universe, reaching Earth from distances of millions, often even billions, of lightyears away. They can last from a few milliseconds to several minutes and are caused by the collapse  of massive stars or the collision of compact astrophysical objects such as neutron stars or black holes. While the stars merge into a black hole in their death struggle, they emit streams of matter, known as jets that accelerate particles of matter to almost the speed of light. In the process, an extremely bright flash of gamma radiation is produced – similar to X-rays – releasing more energy in seconds than our sun does throughout its entire lifespan.

Additionally, the collapse of a single massive star at the end of its life to directly form a black hole leads to an enormous conflagration, known as a supernova or hypernova, whereby again a similar bright flash of radiation is produced. Since US satellites first detected gamma-ray bursts in 1967, they have been intensively studied. However, many questions still remain unanswered. What exactly happens when stars collapse?  How often are gamma rays emitted during such events? Do all jets  have the same structure or do they vary from case to case? Gamma-ray bursts cannot be observed from the Earth’s surface as they are absorbed in its atmosphere. Therefore, space telescopes on board satellites play a crucial role in research. A team from the Institute for Astronomy and Astrophysics at the University of Tübingen has now provided important technology for this research.

Ride-sharing into space

Nanosatellites can have an important advantage over conventional satellites: They can be manufactured more cost-effectively because the developers – as in the Tübingen project – can use off-the-shelf components. Sending nanosatellites into space is also cheaper, as ride-sharing opportunities are used, avoiding rocket launches for each mission. Universities generally do not have the financial means of space agencies and this saving means that they can also make important contributions to research.

Another plus point of the nanosatellite project is its speed, says Guzmán: “In less than five years, we have designed, built, and launched an entirely new miniaturized detector. For doctoral students, it is very attractive to collaborate on such a project that they can accompany up to the launch.” Development and manufacturing large satellites, as is common with ESA or NASA, take significantly longer.

Once SpIRIT has completed its testing phase and proven the capability of the HERMES network, the seven nanosatellites will commence their work. Together, they will scan the sky for gamma-ray bursts and attempt to locate radiation sources more precisely. Detectors on the satellites register the same burst at different times due to their different positions in orbit, which is valuable information for the astrophysicists. Based on this difference, they can calculate where in space the collapsing stars and black holes emitting these bursts are located.

Insights into the history of the universe

Gamma radiation that the HERMES satellites are designed to detect represents only part of this phenomenon. Cosmic events and their aftermath also release other electromagnetic waves: UV and infrared radiation, visible light, and radio waves. To detect them, telescopes are needed that are specialized in specific frequencies.

Another type of wave that does not belong to the electromagnetic spectrum was first detected in 2016: Gravitational Waves. GWs are generated when extremely massive stars or black holes merge. They move at the speed of light through the cosmos, warping the space they traverse. Multi-messenger astronomy aims to capture such diverse physical information through a network of specialized telescopes, identifying them as puzzle pieces of the same event, and assembling them.

Combining different methods and data promises new insights into the formation and history of the universe. For example, questions  exploring the origins of the chemical elements or the speed at which the universe is expanding. Researchers at the institute specialize in one of the trickiest puzzles of cosmology, as Guzmán explains: “The special theory of relativity postulates that all observers in a vacuum measure the same speed of light, regardless of the wavelength of the light, which is related to the notion that space is a continuum.”

If space is divided into units on very small scales, it is conceivable that light could propagate slightly faster or slower in this lattice depending on its wavelength. The differences are far too small to be detected on Earth. However, by observing light rays in the cosmos over a very long time and distance, scientists can measure whether photons really move at different speeds. “Our institute is among the first to try this. The observation of gamma rays through our satellite constellation is excellently suited for this purpose,” says Guzmán.

Text: Wolfgang Krischke