Uniting for big-bang discoveries

Two groundbreaking breakthroughs this week shows the promise of international cooperation in science

Thursday was physics day. Two big announcements were made by different research groups. Gravit­ational wave researchers using pulsars announced they had discovered gravitational signals that might even date back to the Big Bang. Researchers studying neutrinos generated a picture of the Milky Way galaxy as “seen” by these ghost particles.

Taken together, these promise explosive new insights. The technologies developed for these observations were awesome, and so was the spirit of collaborations across frontiers. Both sets of results came from large groups located in many research institutions across multiple nations.

Humans have been looking at the sky for millennia. But visible light is only a small part of the electromagnetic spectrum. Big new discoveries were made when scientists started to use other parts of the spectrum. Radio wave astronomy led to the discovery of pulsars and quasars, and the discovery of the cosmic microwave background radiation, which is evidence for the Big Bang.

Gravitational wave astronomy confirmed the existence of black holes. The latest discovery could help us understand the violent processes of black holes and galactic mergers, and how the Big Bang occurred.

Neutrinos are elementary particles created by violent processes, such as atoms colliding together. They can be created in the lab and occur naturally on much larger scales. These are called ghost particles  because they are electrically neutral and pass straight through solid objects. Stellar neutrinos have much higher energy levels compared to neutrinos created in particle accelerators like the Large Hadron Collider.

In both cases, detection is a problem. Gravitational waves created by the Big Bang are still washing through space, if the theory is right. So are waves from black holes. But these are very long, weak waves and need extremely sensitive gear to detect. The energy neutrinos carry is about the only way to find them, and again, extreme sensitivity is required.

The first detection of gravity waves came from the LIGO (Laser Interferometer Gravitational Wave Observatory), which found its first example of black holes merging back in 2015. LIGO uses a T-shaped detector with each arm measuring 4 km in length. Lasers are fired down these arms with mirrors placed at strategic points. If a gravitational wave passes through, it distorts space by a miniscule amount, resulting in a slight change in the length of the laser beams. LIGO can only pick up signals from gravitational waves of a certain length — around 3,200 km long — whereas super massive black holes emit gravity waves of far longer wavelengths — literally light years long. 

Scientists figured out a way to use pulsars as natural detectors of really long gravity waves. A pulsar is a dead star that rotates at a constant rate, beaming out very regular radio signals. Tiny deviations in the timing of those signals can mean the presence of a gravitational wave. By studying data from 70 pulsars, scientists could isolate times when they were affected by the same wave. Also due to celestial distances, they could identify really long waves.

The most sensitive neutrino detection facility, IceCube, is located at the South Pole. It uses light sensors buried under 2.5 km of ice, where it’s pitch dark. When a neutrino passes through, it emits energy that interacts with the ice, creating a blue radiation called Cherenkov Radiation. Since neutrinos don’t interact with anything or deviate from their path, the energy trail can be used to figure out origin. By mapping those origins, scientists have created a picture of the Milky Way.

This is a very simplified explanation of monstrously complicated data crunching. IceCube picks up 2,700 energy interactions per second from all sorts of particles hitting the ice. It isolates 17 neutrinos per day. Gravitational wave detectors isolate and compare differences of milliseconds in pulsar timings.

Drilling 2.5 km deep holes in ice and figuring out what’s happening at those depths, measuring tiny units of time, machine learning to handle data at these scales — all this requires hundreds of experts working in unison. These technologies will surely find commercial applications, and these research teams set an example for international cooperation that cannot be bettered.