Unveiling the Mysteries of Dark Matter, Dark Energy, and Antimatter (Part II)
In our previous article, we discussed the nature of dark matter and now we'll continue with dark energy and antimatter.
Dark Energy
Image from: NASA Science
Dark energy makes up around 68% of the universe, but even less is known about dark energy than dark matter. What we do know is that dark energy is the mechanism behind the acceleration of the universe’s expansion.
Detection of Dark Energy
So, how was dark energy detected? Observations of distant supernovae showed that the universe expanded more slowly in the past than it does now. The main explanation is that the universe contains something that reverses the gravitational effect where the universe is pushed apart faster and faster instead of being pulled closer to itself - which is dark energy.
Cosmological Redshift
Image from: NASA
Hubble measured the light produced from supernovae of white dwarfs from various galaxies because their precise brightness is known. The measured light is used to derive the exact distances of Earth from the galaxies at various light year distances. It was found that the light from these supernovae were getting redshifted which shows that the galaxies were moving further away.
Not only that, it was observed that detected light from further galaxies was more redshifted, which shows that galaxies farther away from Earth are moving away faster than closer ones. The relationship between the distance of galaxies and their redshift is also exemplified by Hubble's Law. It states that the recessional velocity of a galaxy (how fast it moves away from us) is directly proportional to its distance from us.
Image from: Dutton Institute
Therefore, the accelerated expansion of the universe is believed to be caused by dark energy by studying this relationship and theoretical models like the Lambda Cold Dark Matter (ΛCDM) Model which proves the observed data with dark energy included.
Antimatter
Antimatter is the opposite of matter that was created in equal amounts as normal matter in the Big Bang. Strangely. it has become very scarce in the universe unlike matter that is dominant everywhere. However, although one may think that antimatter is the complete opposite of matter and would rise in response to gravity, its atoms actually fall! Scientists are still trying out to understand why matter and antimatter did not combine and cancel each other out in the beginnings of the universe, leaving nothing but energy.
Antimatter is basically made up of the same particles as matter but they have the opposite charges. Protons become antiprotons (negative charge) while electrons become positrons (positive). So hydrogen for instance, would be called antihydrogen, and have a antiproton in the nucleus and have a positron orbiting it.
Image from: BBC
Unlike dark matter and energy, antimatter can be manufactured in labs on Earth. Antiprotons are created by colliding particles in Cern’s accelerators, and along with the positrons, are sent to a magnet to mix them to form atoms of antihydrogen. These atoms and particles have to be contained using the magnetic field of the huge magnet since antiparticles explode in contact with particles of normal matter, and therefore, cannot be kept in a container.
When the magnetic field is turned off, the antiatoms are released and sensors detect whether they rise or fall. It has been discovered is that they fall downwards which supports Einstein’s General theory of Relativity. However, the speed at which it falls can still be different which opens up doors to more discoveries by using more advanced and sensitive sensors in the future.
Hubble has discovered a globular cluster NGC 2005 located about 750 light-years from the heart of the Large Magellanic Cloud (LMC), which is the Milky Way’s largest satellite galaxy. Globular clusters are groups of stars that are very densely-packed and can hold around millions of stars. Their density makes them stable as they are tightly held together by gravity and can last for long. Some can even be as old as billions of years old! Studying globular clusters in space is similar to studying fossils on Earth, except globular clusters reveal the characteristics of ancient stars.
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