Hey Lykkers, did you know that one of the most groundbreaking discoveries of this century happened just a few years ago?

On February 11, 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced something incredible: the detection of gravitational waves.

This discovery, labeled as GW150914, came from the violent collision and merger of two black holes, each about 30 times the mass of the Sun, located 1.3 billion light-years away. Imagine that! It was the first time humanity had "heard" such a signal, and it marked a huge leap in our understanding of the universe.

Detecting Gravitational Waves: Routine Discoveries Now

Since that historic moment, LIGO, along with Europe's Virgo detector, has identified 50 gravitational wave events. The detection of gravitational waves has become nearly routine, with new events being discovered almost weekly. In fact, scientists now have to add timestamps (hours, minutes, and seconds) to the names of signals, as multiple events can be detected in a single day. It's amazing to think that the tools we use to study the cosmos have become so precise, Lykkers!

How Do These Signals Come About?

All 50 gravitational wave signals detected by LIGO and Virgo so far come from the mergers of two dense celestial objects. These objects—either neutron stars or black holes—are born from the explosive deaths of massive stars. There are two primary ways these binary systems of dense objects can form. One occurs when two massive stars in a binary system both explode as supernovae, creating two dense remnants that are close enough to eventually merge. The other takes place in dense star clusters, where two unrelated dense objects might meet and form a binary system due to gravitational interactions. The dynamics of these events are mind-boggling!

Black Holes and Neutron Stars: Size and Spin Matter

By analyzing the gravitational waves, we can determine the mass and spin of the black holes and neutron stars involved. Most of the 50 detected events so far have been black hole mergers, but there have been a few neutron star mergers as well. Prior to the discovery of gravitational waves, astronomers observed black holes with masses between 5 and 15 times that of the Sun. But when GW150914 was detected, it revealed two black holes with masses of 30 times the Sun's mass, which was a huge surprise!

Special Cases: Unsolved Mysteries

However, some events have puzzled scientists. Take GW190521, for example. In this case, the black holes involved had masses of 85 and 66 times that of the Sun—smack in the middle of an unexpected gap in black hole sizes. This is known as the “black hole mass gap,” and it's something that astronomers are still trying to fully understand. Another interesting event, GW190814, involved one object with 23 times the Sun's mass and another with only 2.6 times the Sun's mass. This sparked a debate over whether the smaller object was the lightest black hole ever detected or the heaviest neutron star.

Gravitational Waves and Multi-Messenger Astronomy

One of the most exciting discoveries came in 2017 with the merger of two neutron stars, GW170817. Not only did it emit gravitational waves, but it also released electromagnetic waves, such as gamma rays, X-rays, and visible light, which made it a multi-messenger event. This allowed astronomers to study the event across multiple wavelengths of light and learn more about the universe's mysteries. Imagine being able to study a cosmic event through both gravitational waves and light waves at the same time—how cool is that?

Understanding the Universe's Expansion

Gravitational waves are also playing a key role in helping scientists measure the rate of the universe's expansion—something known as the Hubble constant. Unlike traditional methods that rely on “distance ladders” (using stars and galaxies to gauge distance), gravitational waves can directly measure the distance between two objects in a merger. For example, the discovery of GW170817, combined with the redshift data from its host system, provided valuable insights into the Hubble constant. With more gravitational wave events, we may have a powerful new tool for solving long-standing mysteries in cosmology.

Testing Einstein's Theory of General Relativity

Another incredible aspect of gravitational waves is their ability to test Einstein's theory of general relativity. When scientists detected GW170817, the gravitational waves arrived only 1.7 seconds after the gamma rays. Given that the source was 1.3 billion light-years away, this allowed scientists to confirm that gravitational waves travel at the speed of light, as predicted by Einstein's theory. So far, no deviations from general relativity have been observed in gravitational wave measurements. It's thrilling to see how the universe continues to confirm our understanding of the laws of physics!

What's Next? The Future of Gravitational Wave Astronomy

Looking ahead, Lykkers, things are going to get even more exciting. The LIGO and Virgo detectors are expected to start their fourth observational run in June 2022, with Japan's KAGRA detector joining the network soon. By 2025, these detectors will reach their design sensitivity, meaning we can expect hundreds of new events to be discovered. As these detectors improve, we might uncover new types of gravitational waves, such as continuous waves or gravitational wave bursts—perhaps even from sources we've never imagined before!

The Universe is Calling

So, Lykkers, we're just at the beginning of an exciting new era in astronomy. Gravitational waves have opened up a whole new way of "listening" to the universe, and as the detectors improve, we can expect even more mind-blowing discoveries. Keep your eyes on the sky, because the mysteries of the universe are just waiting to be uncovered!