Last week, the astronomy community was excited by news released by the National Science Foundation that brought answers to a mystery that was over a century-old. Scientists confirmed the first known source of a high-energy particle called a neutrino. Although various news outlets shared this news worldwide, this post hopes to explain in simple terms how this was discovery was made and what this announcement means for the field of astronomy.
Artist's depiction of a blazar firing high energy particles into space.
Credit: DESY, Science Communication Lab
Firstly, it is important to explain what a neutrino is, as it is this particle that was the subject of the scientific breakthrough. Neutrinos are very small, subatomic particles that exist everywhere. They are similar to electrons, however they do not have a charge (electrons carry a negative charge). These particles also have extremely little mass, so they are often called the "ghost" particle. Due to this small mass, they hardly react with normal matter. This makes them very hard to detect. We know very little about neutrinos, but they are one of the most fundamental and abundant particles in the universe. Millions upon millions of these ghostly particles stream through your body right unnoticed now and all the time. They are everywhere. Because of their nature, neutrinos can pass straight through matter across vast distances without being affected - including space. Wherever neutrinos come from, they can travel far and through anything (like galaxies and anything within them). Even particles of light (called photons) can take tens of thousands of years to crawl through from the middle of a star, but a neutrino can do this in a matter of seconds.
This discovery (in its simplest) revealed that for the first time, we have found one place where high-energy neutrinos come from. Before last week, we had no idea. Neutrinos have high energy and here on Earth we are no stranger to high energy particles. We understand that much of these particles come from the Sun. However, for neutrinos with very high energies, where they come from was not known. Neutrinos are also associate with cosmic rays, which are streams of high-energy radiation, mainly from outside the Solar System and beyond. We have now pinpointed a source for cosmic rays and neutrinos in deep space.
The IceCube Neutrino Observatory was constructed in Antarctica to detect these mysterious particles. Computers here collect information from sensors that are positioned deep inside the ice to look for light that is emitted when a neutrino hits its very delicate detectors. These detectors are positioned 2.5 kilometres under the ice so that any other particles do not interfere with the data. This means that the ice only allows neutrinos to pass through it to reach the sensitive sensors (since neutrinos can travel through anything). The facility has already contributed greatly to neutrino research. For example, in 2013 the observatory confirmed for the first time that they had detected neutrinos from beyond the Milky Way galaxy. At the time, researchers could not pin down the source of those high-energy ghost particles more precisely.
The South Pole's IceCube Neutrino Observatory in Antarctica
(Credit: Sven Lidstrom, IceCube/NSF)
The July 12th announcement revealed that on September 22nd, 2017, the detectors had been hit by another high-energy neutrino. This time, the team wanted to find out where it came from. A notification was sent to astronomers around the world with the coordinates of the angle from which the neutrino hit the detector. This allowed researchers to carefully pinpoint their telescopes and equipment to these coordinates to look for anything that might exist in this exact location that could have been the neutrino's source.
Roughly twenty space and ground-based telescopes searched this point in the sky (in the constellation Orion) across different wavelengths, from gamma-rays to radio-waves. What they found to exist in this location was a "blazar" already known (called TXS 0506+056) that is located roughly 4 billion light-years from us. Amazingly, researchers were able to track the single cosmic neutrino to this one blazar: a huge elliptical galaxy with a fast-pinning supermassive black hole at its heart that is firing beams of energy toward Earth.
This means that 4 billion years ago, a single neutrino began soaring through space from this blazar. It might have passed through planets, galaxies, and stars on its way to us. Remember: neutrinos can stream through matter without leaving any trace. Together with observations and data from the other observatories, the team was able to confirm the first known source of the mysterious neutrino. Blazars may not be the only source, but they are the first that we have evidence for. Astronomers know of many many blazars that exist, but this is the first one that seems to be firing neutrinos our way like this one.
Findings like this are important in astronomy because they can help us narrow our research. Space is big, so any findings that help us pinpoint an area of understanding is very helpful. Now, researchers can look more into blazars to learn more about the origin and nature of the mysterious neutrino particles. They are everywhere and can travel through everything, so naturally it is important to understand them. Astronomers now have a set of new questions they wish to answer. For example, many are now curious of how blazars like this can accelerate particles to such extremely high energies through space. More events and breakthroughs such as this will help us create a more complete understanding of the universe, particularly about the extremely powerful events and objects in the sky.
The findings results were published in the journal Science and can be found here or here.