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Large scale structure of light distribution

Scientists conduct experiment to define constraints on the force of dark energy

It is now well established through observations that the universe is expanding which has been speeding up over time. However, the cause of the expansion is not yet known. It is assumed to be a mysterious energy acting opposite to gravity causing this expansion.

This energy is termed as “dark energy” and it is estimated that it makes up to 72 percent of the constituents in the universe. A new experiment has confirmed that it is not a new force. The study appears in the Physical Review Letters journal. Ed Copeland, a physicist from the University of Nottingham said that the experiment related to cosmology and atomic physics helped in ruling out several models which have been proposed for the explanation of dark energy and will eliminate many more models.

There are four fundamental forces in the Universe which are gravity, electromagnetic force, strong nuclear force and weak nuclear force. Some anomalies do not fit into the current model of how the Universe functions. So they are clubbed under a fifth hypothetical force.

These anomalies have helped in putting constraints on the fifth force and helped in constructing alternatives to general relativity for explaining the increasing rate of expansion of the Universe. Some of the alternatives are chameleon theory and symmetron theory.

If another force present in the Universe was responsible for almost 75 percent of its mass-energy density then it should be easy to detect. But if it acts opposite to gravity i.e. a repulsive force then it should be weakest in the area where gravity is the strongest force. This should hold true for objects with significant mass such as a planet.

An experiment was designed to observe this anti-gravitational force. Within a sealed vacuum chamber, a large aluminium sphere and small weights – atoms of rubidium-87 were placed and atom interferometry was used for measuring the acceleration of the smaller weight towards the larger one. If a fifth force was present then the atom should have been veered off its path as it moved towards the sphere. But no such deviation was observed which clearly explains that no such anti-gravity force was present in the chamber. It does not mean that there is no fifth force at all. However, the force can be defined by several constraints which also means that similar constraints can be placed on chameleon and symmetron theories.

There may not be always a straightforward answer to fundamental questions of this nature so the correct questions are asked to narrow down on the correct answer. Answering this question would give significant answers about the evolution of the universe.

Journal Reference: Physical Review Letters

gravity anomaly moon

Researchers detect mass anomaly under largest crater of moon

A largely massive material was discovered under the largest crater of our very solar system, the Moon’s South Pole-Aitken basin. This appears to be quite mysterious as it contains metals from an asteroid that had crashed into the moon, resulting in the huge crater as per a study by the Baylor University.

Envisage a situation wherein you take a pile of metal, approximately five times larger than the islands of Hawaii and bury it. The discovery of the mass was as unexpected as this hypothetical situation. The crater is oval in shape and is nearly 2,000 kilometres wide, which is roughly the distance between Delhi and Bangalore. Although it is very large, it’s quite unlikely that you might get to see it.

According to the study “Deep Structure of the Lunar South Pole-Aitken Basin” published in the journal Geophysical Research Lettersin order to measure the subtle changes in the power of gravity around the Moon, scientists had to analyse a huge amount of data from spacecrafts which have been used for National Aeronautics and Space Administration (NASA) Gravity Recovery and Interior Laboratory (GRAIL) mission.

The dense mass along with its mysterious existence weighs the basin floor downward by more than half a mile. Computer simulations of the existing large asteroid impacts suggested that under the right conditions, an iron-nickel core of an asteroid can get dispersed in the upper mantle.

“We did a lot of math and it showed that a sufficiently dispersed core of the asteroid that made the impact could remain suspended in the Moon’s mantle until this present day, instead of just sinking to the core of the Moon, like other asteroids,”  Peter B. James, the co-author remarked.

Another possibility of the existence could be that the mass is the concentration of dense oxides linked to the last stage of lunar magma solidification. He thinks that the South Pole -Aitken basin has been created about 4 billion years ago and it has been preserved since then. Though many impacts have occurred throughout the solar system, it has lost most of its traces with the course of time.

James refers to the basin as one of the best pre-existing natural laboratories for studying destructive impact cases which refers to the age-old process which shaped the solar system as we see it.

This research work was supported through the NASA Gravity Recovery and Interior Laboratory (GRAIL) science team and a team of intelligent, like-minded investigators and researchers hailing from GRAIL.

ESO VLT Laser taking Milky Way photo

Milky Way’s new mass calculated

The new calculation of the measurement of the size and mass of the Milky Way is more accurate and the galaxy turned out to be more massive than thought earlier.

The galaxy has been calculated to have a mass of about 1.5 trillion Sun’s worth of mass (solar masses) within a radius of around 129,000 light years. This calculation exceeds over twice as much as previous estimates of 2016’s study in which it was estimated to have around 700 billion solar masses.

To accurately map the Milky Way in three dimensions, ESA’s Gaia Mission has been launched. This mission has given the most detailed map of our home galaxy ever made and has been refining our knowledge all over the shop.

A search team has been able to infer the galaxy’s size and mass based on the orbital motion of groups of stars called globular clusters, out in the galactic halo by combining Gaia data with those from Hubble Space Telescope observations.

Hubble Telescope

The Hubble Space Telescope as seen from the departing Space Shuttle Atlantis, flying STS-125, HST Servicing Mission 4. Image Credit: Wikimedia/ Ruffnax (Crew of STS-125)

With the dark matter in play, the mass of the Milky Way can’t just be guessed based on what we can see. And the dark matter cannot be detected directly. But there is an assumption that something is out there, because of the orbital velocity of the outer region of the galaxy.

The matter orbits much faster than it should, based on the matter that can be detected – as though something, some undetectable mass, is creating extra gravity in the Universe.

It is important to infer its mass based on other methods because the dark matter can’t be observed directly. By starting with that outer-galaxy orbital velocity, astrophysicists can work backward to calculate the mass responsible, based on Kepler’s laws of orbital motion.

On the same subject, Gaia and Hubble are dedicated to working. It has been 10 years since they have been combined. And they have provided more accurate measurements of the orbital motion of globular clusters in the outer reaches of the Milky Way.

“The more massive a galaxy, the faster its clusters move under the pull of its gravity,” said astrophysicist Wyn Evans of the University of Cambridge in the UK.

“Most previous measurements have found the speed at which a cluster is approaching or receding from Earth that is the velocity along our line of sight. However, we were able to also measure the sideways motion of the clusters, from which the total velocity, and consequently the galactic mass, can be calculated.”

On this basis, the team reached the 1.5 trillion solar masses figure. But the thing is that there are only about 200 billion stars in the galaxy. Sagittarius A*, the supermassive black hole at the galactic center, accounts for another 4 million solar masses. And there’s a bunch of dust and gas. But all that concludes around 90% of the mass meaning, there is the dark matter that is yet to be found out.

“We want to know the mass of the Milky Way more accurately so that we can put it into a cosmological context and compare it to simulations of galaxies in the evolving universe,” explained physicist Roeland van der Marel of the Space Telescope Science Institute in the US.

The Milky Way galaxy has been noted to be in an intermediate range according to the new measurements put it at a pretty healthy size and mass for its class, but the extra heft doesn’t even put us near the biggest galaxies – those are in the range of 30 trillion solar masses.

For many years, the Milky Way has been thought to the biggest galaxy in nearby intergalactic space was Andromeda, with the Milky Way coming in second.

But according to Andromeda’s new calculations last year, the Milky Way was put to be at around 800 billion solar masses which could mean that it is actually number one – and has been all along.
And so, rather than the other way around as we previously thought, it could mean that Andromeda gets subsumed into the Milky Way when the pair collide in 4.5 billion years.