Dark matter

 Dark matter

Roughly 80% of the mass of the universe is made up of material that scientists cannot directly observe , known as dark matter. This bizarre ingredient does not emit light or energy. Since atleast the 1920s , astronomers have hypothesised that the universe contains more matter than seen by the naked eyes. Support for dark matter has grown since then, and although no solid direct evidence of dark matter has been detected, there have been strong possibilities in recent years.

Originally known as the , "missing mass", dark matter's existence was first inferred by Swiss American astronomer Fritz Zwicky, who in 1933 discovered that the mass of all the stars , in the coma cluster of galaxies provided only about 1% of the mass needed to keep the galaxies from escaping the cluster's gravitational pull.

Two varieties of dark matter have been found to exist. The first variety is about 4.5% of the universe and is made of the familiar baryons. Most of the baryonic or ordinary component of dark matter has been determined by measuring the abundance of elements heavier than hydrogen that were created in the first two minutes after the big bang occurred 13.8  billion years ago.

Dark matter exits or not

Scientists have not yet observed dark matter directly. It doesn't interact with baryonic matter and it's completely invisible to light and other forms of electromagnetic radiation, making dark matter impossible to detect with current instruments. But scientists are confident it exists because of the gravitational effects it appears to have on galaxies and galaxy clusters.

Scientists have a few ideas for what dark matter might be. One leading hypothesis is that dark matter consists of exotic particles that doesn't interact with normal matter or light but still exert a gravitational pull. Several scientific groups ,including one at CERN's Large Hardron Collider ,are currently working to generate dark matter particles for study in the lab.

Physicists categorize these under the broad description, "Weakly Interacting Massive Particles " or WIMPS. These heavy particles wouldn't interact with electromagnetic charges,but could still swap details with normal matter through the weak nuclear force.

Rather than being made of a new kind of material, dark matter could simply be ordinary objects that act in extraordinary ways. Massive astrophysical compact halo objects (MACHOS) are one candidate, heavy star like bodies that just don't glow enough.

Since the confirmation of dark matter 's existence, a preponderance of dark matter in galaxies and clusters of galaxies have been discerned through the phenomenon of gravitational lensing - matter acting as lens by bending space and distorting the passage of background light. Albert Einstein showed that massive objects in the universe bend and distort light, allowing them to be used as lenses. By studying how light is distorted by Galaxy clusters, astronomers have been able to create a map of dark matter in the universe. All of these methods provide a strong indication than most of the matter in the universe is something yet unseen.

The Bullet Cluster is considered a crucial piece of evidence for the existence of dark matter. It is famous for being the first galaxy merger to be deeply studied ,but astronomers have since found many more galaxy mergers that show the same dark "lobe" structure.

Scientists posited that these massive compact halo objects ( or "MACHOs") could make up the missing matter.

Some of the strongest candidates for dark matter - which would explain abnormal galaxy rotation speeds,the Bullet Cluster, BAOs and the large - scale structure of the universe are Weakly Interacting Particles (or " WIMPs") . But so far ,thorough, decades ,long searches ,have not yet turned up any evidence for the existence of WIMP dark matter candidates; instead, they have set stricter and stricter limits on their possible properties.

A dark matter theory has so much to explain and as experiments get more precise and telescopes get sharper,we may be able to cross  a few more off our list.