SpaceWatch: Tales of matter and diamonds

The matter of the Universe?

Astronomers in the US say they have precisely measured the total amount of matter in the Universe, concluding that it makes up 31.5%, give or take 1.3%, of all matter and energy.

The rest, the team led by the University of California Riverside (UCR) reports in a paper in the Astrophysical Journal, is dark energy.

“To put that amount of matter in context, if all the matter in the Universe were spread out evenly across space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic metre,” says first author Mohamed Abdullah.

“However, since we know 80% of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don’t yet understand.”

The new figure is actually a “best combined value” of the UCR-led measurements and those from other teams using different techniques.

Abdullah and colleagues first developed GalWeight, a tool to measure the mass of a galaxy cluster using the orbits of its member galaxies, then applied it to observations from the Sloan Digital Sky Survey (SDSS) to create GalWCat19, a publicly available catalogue of galaxy clusters. 

Finally, they compared the number of clusters in their new catalogue with simulations to determine the total amount of matter in the Universe.

“We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique,” says co-author Gillian Wilson.

“Moreover, this is the first use of the galaxy orbit technique which has obtained a value in agreement with those obtained by teams who used non-cluster techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing.”

Not a quasar, but bright enough

Astronomers have found what they say is the first galaxy with ultraviolet luminosity comparable to that of a quasar.

In fact, BOSS-EUVLG1 previously was classified as a quasar in the BOSS (Baryon Oscillation Spectroscopic Survey) project on the strength of that luminosity and its large redshift value – the measure of the reddening of the light coming from a galaxy – of 2.47.

However, new observations made with the Gran Telescopio Canarias (GTC) in the Canary Islands and the Atacama Large Millimetre / submillimetre Array (ALMA) in Chile reveal that it is a galaxy with extreme and exceptional properties.

Writing in the Monthly Notices of the Royal Astronomical Society Letters, the researchers say the high luminosity of BOSS-EUVLG1 in the ultraviolet and in Lyman-alpha emission is due to its large number of young, massive stars – well above the range for other galaxies.

The rate of star formation is very high: around a thousand times higher than that in the Milky Way, although the galaxy is 30 times smaller.

“This rate of star formation is comparable only to the most luminous infrared galaxies known, but the absence of dust in BOSS-EUVLG1 allows its ultraviolet and visible emission to reach us with hardly any attenuation”, says co-author Ismael Pérez Fournon.

The results of the study suggest BOSS-EUVLG1 is an example of the initial phases of the formation of massive galaxies.

The story of cosmic diamonds

Ureilites are a special type of meteorite that often contains diamonds. It has not been clear, however, how those diamonds came to be.

It is unlikely they formed when meteoroids hit the Earth, as impact events with such vast energies would make the meteoroids evaporate completely. It has therefore been proposed that larger diamonds – similar to those in the Earth’s interior – must have been formed by continuous pressure in the interior of planetary precursors the size of Mars or Mercury.

A new and truly international study now suggests otherwise, after scientists from Germany, Italy, the US, Russia, Saudi Arabia, Switzerland and Sudan analysed the largest diamonds ever discovered in ureilites from Morocco and Sudan.

Writing in the journal Proceedings of the National Academy of Sciences, they report that the formation of diamonds in ureilites does not require a Mars-sized parent body, which has significant implications for planetary formation models.

“Our extensive new studies show that these unusual extra-terrestrial diamonds formed through the immense shock pressure that occurred when a large asteroid or even minor planet smashed into the surface of the ureilite parent body,” says Frank Brenker, from Germany’s Goethe University.

“It’s by all means possible that it was precisely this enormous impact that ultimately led to the complete destruction of the minor planet.

“This means – contrary to prior assumptions – that the larger ureilite diamonds are not a sign that protoplanets the size of Mars or Mercury existed in the early period of our solar system, but nonetheless of the immense, destructive forces that prevailed at that time.”

Modelling the consequences of collision

Earth could have lost anywhere from 10% to 60% of its atmosphere in the collision that is thought to have formed the Moon, a new study suggests.

Researchers led by Durham University in the UK ran more than 300 supercomputer simulations to study the consequences that different huge collisions have on rocky planets with thin atmospheres.

They say the findings, published in the Astrophysical Journal Letters, have led to the development of a new way to predict the atmospheric loss from any collision across a wide range of rocky planet impacts that could be used by scientists who are investigating the Moon’s origins or other giant impacts.

They also found that slow giant impacts between young planets and massive objects could add significant atmosphere to a planet if the impactor also has a lot of atmosphere.

“While these computer simulations don’t directly tell us how the Moon came to be,” says lead author Jacob Kegerreis, “the effects on the Earth’s atmosphere could be used to narrow down the different ways it might have been formed and lead us closer to understanding the origin of our nearest celestial neighbour.”

Previous work at Durham examined the ways that thin atmospheres could be removed by objects impacting at different angles and speeds. The new paper looks at the effects across a wider variety of impacts adjusting for size, mass, speed and angle of the impacting object.

The simulations revealed the different outcomes when one or more of these variables are changed, leading to atmospheric loss or gain, or sometimes the complete obliteration of the impacted planet.

Cross-section animation of the early stages of a 3D simulation of a head-on, slow giant impact using 30 to 100 million particles. Credit: Jacob Kegerreis, Durham University.