The Universe is made up of two fundamental elements: matter and energy. The fact that most of the matter in the universe is invisible and the origin of the majority of the energy is not well understood presents scientists with a significant challenge. If we can’t see the majority of the Universe, how can we study it?

Researchers at the Center for Astrophysics | Harvard & Smithsonian will remain at the forefront of the study of dark matter and dark energy as our observational methods advance.

The distribution of dark matter in galactic clusters that are colliding, like the Bullet Cluster, is being mapped with the aid of NASA’s Chandra X-ray Observatory and optical telescopes. Although gravitational lensing measurements reveal that dark matter was unaffected by the collision and separated from the normal matter, X-ray observations reveal a heated shock front where the gas from the clusters collided and slowed down.

Some dark matter particles are thought to annihilate and vanish in a flash of extremely high-energy radiation when they collide. The signature of dark matter annihilation is being sought after by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) in Arizona, which can detect gamma radiation.

Limits on dark energy are being set by Chandra and the South Pole Telescope in Antarctica by observing how galaxy cluster evolution has changed over the course of the Universe’s history. Researchers are investigating how dark energy and gravity competed throughout the history of the Universe by contrasting observations of galaxy clusters with experimental models.

Leading the Baryon Oscillation Spectroscopic Survey (BOSS), which examined millions of Galaxies and plotted their distribution in the universe, were researchers at CfA. The distribution, where some areas have more galaxies and others have fewer, has been demonstrated to mimic sound waves from the early Universe. We can measure the distance to galaxies and map the effects of dark energy more precisely by looking at these distributions.

A 3D map of the Universe with millions of galaxies out to 10 billion light years is on the horizon thanks to the Dark Energy Spectroscopic Instrument (DESI). This map will track the impact of dark energy on the universe’s expansion. Additionally, by observing billions of galaxies and finding an unprecedented number of supernovae, the Large Synoptic Survey Telescope (LSST) will be able to constrain the characteristics of dark matter and dark energy.

Dark Matter and Dark Energy

The disparity between a cluster of galaxies’ motions and the amount of visible matter within it was first identified by astronomer Fritz Zwicky. He proposed that there might be “dark matter,” or invisible matter that interacts gravitationally with visible matter. Similar anomalies were later discovered by astronomers while studying nearby spiral galaxies. The fact that the galaxies’ outer edges rotated much faster than anticipated suggests that “dark matter” permeated the entire galaxy and extended beyond it.

The way dark matter affects the way light from a background source bends allows us to estimate the amount of dark matter in a galaxy. We can gauge the galaxy’s mass by measuring how severe that bend is using this “gravitational lensing” method. We know dark matter must exist when the mass we determine from the bend and the mass we can directly observe do not agree.

According to recent estimates, dark matter makes up about 27% of the universe. Although we don’t yet know what it is, we are looking for solutions.

Since the early 20th century, we have known that the universe is expanding. However, recent observations of far-off supernovae and other observations demonstrate that the expansion of the Universe is not only continuing but accelerating. Because of the gravitational pull of galaxies and clusters of galaxies, this amazing discovery came as a complete surprise because the expansion of the universe should slow down over time. The “dark energy” that is necessary to explain this observation has been dubbed and, according to current models, makes up about 68% of the universe.

The portion of the universe that is still visible to us is only 5%.

What We Know and What We Think

Although we can’t see dark matter, we are aware that it exists. Additionally, we can use gravitational lensing to look into some of the characteristics of dark matter. This method calculates the gravitational pull galaxies have on light coming from farther-off sources. We can learn more about the quantity, density, and distribution of dark matter in a specific lensing galaxy thanks to the warping and magnification of this light. The existence of WIMPs, or Weakly Interacting Massive Particles, is the best theoretical explanation we currently have for the existence of dark matter. Although it should be possible to observe these hypothetical particles and their byproducts directly, doing so has so far proven to be challenging.

Regarding dark energy, Einstein made the assumption that the universe was stationary and neither expanding nor contracting. Because the universe was supposed to be dynamic according to his Theory of General Relativity, he added a “cosmological constant” to counteract gravity. After Hubble revealed that the universe was expanding, he later referred to it as the “biggest mistake” of his life.

The realisation that the universe is expanding faster has brought back interest in the cosmological constant. The most straightforward explanation for this constant is that it stands for the energy of void space. This “vacuum energy” permeates all of space and time without changing.

Dark energy may also be an energy field that changes over time and space, according to another theory. Or it’s possible that we don’t fully comprehend gravity. On very large scales, it might behave differently, for instance. General Relativity has been modified, and astronomers are currently testing these modifications to see if they can account for the universe’s accelerating expansion.

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