3 min read

Using All of Our Senses in Space

From detecting gravitational waves to combining those signals with light, scientists have been making strides in the field of multimessenger astronomy.

But wait – what is multimessenger astronomy? And why is it a big deal?

People learn about different objects through their senses: sight, touch, taste, hearing and smell. Similarly, multimessenger astronomy allows us to study the same astronomical object or event through a variety of “messengers,” which include light of all wavelengths, cosmic ray particles, gravitational waves, and neutrinos – speedy tiny particles that weigh almost nothing and rarely interact with anything. By receiving and combining different pieces of information from these different messengers, we can learn much more about these objects and events than we would from just one.

This animation runs through slides showing the different types of light, their characterizations like wavelength, and where that light might be observed in a city like Seattle. For radio light, the wavelength can be the size of a building, and is seen emanating from radio towers in the city. Microwave wavelengths are about the size of a honeybee and are seen in the sky and from small sites throughout the city. Infrared wavelengths are the size of a cell and the city glows in infrared light. Optical light has wavelengths the size of bacteria and it’s the light that’s reflected from the buildings of the city. Ultraviolet light has wavelengths the size of molecules and is primarily seen from the Milky Way sky. X-rays have wavelengths the size of oxygen atoms and are mostly seen as a background glow in the sky but can also be seen as flashes where in use by medical professionals across the city. Gamma rays have wavelengths the size of atomic nuclei and are seen in a background glow in the sky. Light like X-rays and gamma rays don’t make it through Earth’s atmosphere.
This animation depicts the electromagnetic spectrum and the different characteristics of each wavelength type, from microwaves to gamma rays.
NASA's Goddard Space Flight Center/Conceptual Image Lab

Lights, Detector, Action!

Much of what we know about the universe comes just from different wavelengths of light. We study the rotations of galaxies through radio waves and visible light, investigate the eating habits of black holes through X-rays and gamma rays, and peer into dusty star-forming regions through infrared light.

Earth turns slowly in the background of this animation as the Fermi spacecraft flies in its orbit. Fermi is a shaped like a large gray box with long, blue solar panels extending from either side of the box. Particles and gamma rays, shown as squiggles of gray and magenta, respectively, fly from right to left across the screen, with a few gamma rays getting detected by Fermi.
In this animation, NASA's Fermi Gamma-ray Space Telescope detects gamma rays (magenta) sent to Earth from a supermassive black hole in the heart of a distant galaxy. Some of the same processes that generate the gamma-ray emission also produce high-energy neutrinos (gray), ghostly particles that rarely interact with matter.
NASA's Goddard Space Flight Center/Conceptual Image Lab

The Fermi Gamma-ray Space Telescope studies the universe by detecting gamma rays – the highest-energy form of light. This allows us to investigate some of the most extreme objects in the universe.

When this animation opens, there are concentric rings of pale blue the expand away and off the screen. At the center is a bright ball of light with two narrow cones of orange, fiery-looking material extend in opposing directions, tilted just to the right. During the first few seconds, there are magenta flashes of light that seem to be pushed along with the ends of the orange cones. The central ball expands into a puffy, electric blue cloud. The sequence represents the events that happened after two neutron stars merged, exploding in a gamma-ray burst.
This animation captures phenomena observed over the course of nine days following the neutron star merger known as GW170817, detected on Aug. 17, 2017. They include gravitational waves (pale arcs), a near-light-speed jet that produced gamma rays (magenta), expanding debris from a kilonova that produced ultraviolet (violet), optical and infrared (blue-white to red) emission, and, once the jet directed toward us expanded into our view from Earth, X-rays (blue).
NASA's Goddard Space Flight Center/CI Lab

In 2017, Fermi was involved in two multimessenger firsts. In August it detected the very first light from a gravitational wave source, two merging neutron stars. In that instance, light and gravitational waves were the messengers that gave us a better understanding of the neutron stars and their explosive merger into a black hole.

Multimessenger Astronomy is Cool

This animation begins on a shot of the Orion constellation with a rain of small white particles and small magenta wiggles, representing neutrinos and gamma rays, respectively, travelling from the constellation on the right off the left of the screen. The camera then follows some of the light and particle “rain” to reveal they are traveling toward Earth. Some of the rain passes by Earth while a few of the white particles run into the ice of Antarctica.
Gamma rays (magenta) and elusive particles called neutrinos (gray) formed in the jet of a distant active galaxy. The emission traveled for about 4 billion years before reaching Earth, as shown in this animation. On Sept. 22, 2017, the IceCube Neutrino Observatory at the South Pole detected the arrival of a single high-energy neutrino.
NASA's Goddard Space Flight Center/Conceptual Image Lab

Then, in September of that same year, it helped to combine another pair of messengers – light and neutrinos.

The IceCube Neutrino Observatory lies a mile under the ice in Antarctica and uses the ice itself to detect neutrinos. When IceCube caught a super-high-energy neutrino and traced its origin to a specific area of the sky, they alerted the astronomical community.

Fermi completes a scan of the entire sky about every three hours, monitoring thousands of blazars among all the bright gamma-ray sources it sees. Blazars are galaxies with supermassive black holes at their centers, and some of the material near the black hole shoots outward in a pair of fast-moving jets. In blazars, one of those jets points directly at us!

For months Fermi had observed a blazar producing more gamma rays than usual. Flaring is a common characteristic in blazars, so this did not attract special attention. But when the alert from IceCube came through about a neutrino coming from that same patch of sky, and the Fermi data were analyzed, this flare became a big deal!

This animation shows a cone of blue light travelling across the screen. As it travels, it passes the IceCube detectors that look like long, straight strings of beads. Some of the beads light up, indicating where the cone of light was picked up by the detectors.
When a neutrino interacts with the clear Antarctic ice, it produces secondary particles that leave a trace of blue light as they travel through NSF’s IceCube detector, as illustrated here.

IceCube, Fermi, and follow-up observations all linked the neutrino to a blazar called TXS 0506+056. For the very first time, this event connected a neutrino to a supermassive black hole.

Why is this such a big deal? And why haven’t we done it before? Detecting a neutrino is hard since it doesn’t interact easily with matter and can travel unaffected great distances through the universe. Neutrinos are passing through you right now and you can’t even feel a thing!

This animated GIF opens with us looking over a dark, dusty, donut-shaped cloud of material with a glowing red disk embedded in the over-sized donut hole. Our view changes to show the glowing disk face-on. The glowing material is dark red at its outer edge with the color changing from red to orange to yellow, and finally, to white at the center. Unseen in this image is a black hole right at the center of that disk. Rising from the disk is a white, narrow beam of particles that are being accelerated away. At the end, the base of the disk nearest to the jet pulses and a knot of light travels away from the disk along the jet.
This animation shows the central supermassive black hole of a blazar. The black hole is surrounded by a bright accretion disk and a darker torus of gas and dust. A bright jet of particles emerges from above and below the black hole. Collisions within the jet produce high-energy photons such as gamma rays. A flare from the blazar results in an additional burst of gamma rays and neutrinos.
NASA's Goddard Space Flight Center/Conceptual Image Lab

The neat thing about this discovery – and multimessenger astronomy in general – is how much more we can learn by combining observations. This blazar/neutrino connection, for example, tells us that it was protons being accelerated by the blazar’s jet. Our study of blazars, neutrinos, and other objects and events in the universe will continue with many more exciting multimessenger discoveries to come.