How Do Gamma-Ray Telescopes Measure Distant Stars?

The gamma-ray telescope has been instrumental in expanding humanity’s understanding of the universe’s most profound mysteries.

Astronomers use this sophisticated contraption to study distant space objects at specific wavelengths along the cosmos' electromagnetic (EM) spectrum. Explore the inner workings of these devices and how they’re shaping macrocosmic extrapolation.

Understanding Gamma Rays 

Gamma rays are the highest-energy form of light — or photons — that exist in the universe and are emitted by some of the most extreme sources. They also have the shortest wavelength of light in the EM spectrum. On Earth, humans produce these photons in nuclear facilities, buthey also occur through radioactive decay and lightning. In space, intensely violent events like exploding stars, black holes, solar flares and super bright quasars create them.

The ionising radiation from gamma rays is so powerful that it takes at least 6.6 feet of concrete or 1.3 feet of solid lead to block it. Thankfully, the Earth’s atmosphere filters much of the rays from outer space — otherwise, there wouldn't be any life on the planet. 

The Emergence of Gamma-Ray Telescopy

Unlike the light you can see when you flip a switch, gamma rays can only be detected using specialised sensors. If you tried to observe them using regular lenses and mirrors, the rays would pass right through.

Gamma rays are even more challenging to observe in the vast expanse of space, as they are almost impossible to focus on in any practical way. Astronomers have to employ advanced detection systems to measure the presence of these interstellar events, which led to the invention of the gamma-ray telescope.

Telescopic Evolution

The first version was developed in 1961 and has undergone various design, functionality and placement changes through the years. The most recent adaptation is NASA’s Fermi Gamma-ray Space Telescope, launched into space in June 2008.

Fermi orbits the Earth, scanning the sky every three hours for high-energy cosmic rays and their sources. Since its launch, the telescope has discovered over 300 gamma-ray pulsars, light from the merger of two neutron stars and giant flares beyond the Earth’s Milky Way galaxy. Like the International Space Station, Fermi resides in a low-Earth circular orbit, meaning it needs to move at 17,500 miles per hour to overcome gravity's pull.

Enhancing Gamma-Ray Astronomy

Gamma-ray detection systems have been fundamental to discovering supercharged particles from interstellar explosions called gamma-ray bursts (GRB). These by-products of exploding stars leave a distinct trail that can be detected using telescopes with the right calibrations. Gamma-ray telescopes have observed GRB from extreme events so distant that the light took 13 billion years to reach Earth.

Essentially, these devices allow astronomers to study the universe using cosmic explosions. For example, they can observe the emission components and compare them to results observed in another galaxy. Additionally, the captured data may reveal insights about the stars' unique properties. With over 100 billion stars in the galaxy, there’s no shortage of study subjects.

Tracking gamma-ray bursts also further humankind’s understanding of the past on a celestial level. The ability to study astrophysical objects billions of light years away presents a way to look back in time and uncover hidden fundamental chapters of the universe’s history — perhaps even its origin.

How Do Gamma-Ray Telescopes Work?

Gamma-ray detection in space works slightly differently from other astrological telescopic devices. Using Fermi as a study model, here’s a quick look into the operations of a gamma-ray telescope.

The device comprises two primary instruments — a gamma-ray bursts monitor (GBM) and a large-area telescope (LAT). The GBM looks for high-energy transients above predefined levels, which can indicate the presence of gamma-ray bursts.

Mounted above it is the LAT — a pair conversion telescope that provides higher energy observations across the sky. It is equipped with layers of silicon detectors that split the gamma rays into electrons and positrons on their way down to the specialised detector below. The data from this process enables astronomers to measure the energy of the charged particles and reconstruct their direction over an estimated period.

Applications Beyond Distant Stars

Data gathered by gamma-ray telescopes has been instrumental in measuring vast distances across the universe. GRBs release so much energy that they create optical light curves that are too far away for conventional detectors. Additionally, these curves are too complex, making it difficult to find a pattern.

Gamma-ray telescopes can bridge this gap by providing observed data to improve astronomers' understanding of space. In recent research involving measurements from 500 optical light curves, scientists discovered 180 with a common pattern.

This indicates the GRBs were close enough that the team could calculate the distance between them based on their observed and actual brightness. With further research, this discovery may lead to the creation of novel approaches to studying the universe's expansion rate.

Multi-Messenger Collaboration

GRB detection can also improve multi-messenger collaboration. This branch of astronomy coordinates different cosmic signals to understand space data analytics better. It’s like having various types of detectives work together on the same case, comparing notes and sharing progress updates for a more organised collective effort.

Instead of relying on just one kind of signal — like light or radio waves — scientists study cosmic events using signals such as light, gravitational waves, neutrinos and now, gamma rays. By combining these signals, they can paint a more complete picture of what's happening in the universe and understand phenomena that would be impossible to see with just one type of observation.

Theoretical Advancements

Cosmic gamma-ray measurements have been the foundations of theories on many subjects, including gravity, dark matter and hypernovas. As the telescopes capture more data, many of these theories will likely advance or become refuted, allowing researchers to modify their approach to understanding what makes the universe tick.

Explore Gamma-Ray Astronomy

Gamma-ray telescopes have been essential in unveiling the mysteries of the universe. Astronomers rely on their images to determine crucial information about space objects, including distant exploding stars, galaxies and black holes. Looking ahead, these systems will be vital to further discoveries and insights into the complex nature of the cosmos.