Century of Λ

Century of Λ

ABSTRACT: The cosmological constant was proposed 100 years ago in order to make the model of static Universe, imagined then by most scientists, possible. Today it is the main candidate for the physical essence causing the observed accelerated expansion of our Universe. But, as well as a hundred years ago, its nature is unknown. This paper is devoted to the story of invention of Λ by Albert Einstein in 1917, rejection of it by him in 1931 and returning of it into the science by other scientists during the century.

Einstein’s denial of λ

In the paper On the cosmological problem of general relativity published in 1931 Einstein notes that the static solution is obtained from the Friedmann equations for R which is constant in time and space. However with the help of these equations, one can show that this solution is unstable. It means, that any solution, which at some moment of time is slightly different from the static, will over time be more and more different from it. Already for this reason, without telling as for the results of Hubble’s observations, I do not consider it possible to attribute the physical meaning to my previous solution. In this connection one can ask whether it is possible to describe the observations without introducing a λ-term that is clearly contradictory from the theoretical point of view. In this paper and in the next one with de Sitter published in 1932 he showed that it is possible.

In addition to the second edition of The Essence of the Theory of Relativity published in 1945 Einstein wrote: The introduction into the gravitational equations of the cosmological term is possible, albeit in terms of the theory of relativity is not logically necessary. As Friedmann showed for the first time, the density of matter that is finite everywhere can be reconciled with the first form of equations of gravity, assuming that the metric distance between two material points change over time. Already one requirement of spatial isotropy of the Universe leads to the scheme of Friedmann. There is no doubt that this is the most general scheme that gives a solution to the cosmological problem.

In a letter to Lemaitre, written on 26 August 1947, we find: Since I introduced this constant, I was accompanied by a sense of unclean consciece. … I believe that it is actually very ugly … and I can not believe that such ugly thing could have been realised in nature.

However, the history of the λ-term did not end there. It was destined to have a long and interesting “life”. Steven Weinberg noted in his book Cosmology published in 2008: Einstein’s mistake was not that he introduced the cosmological constant – it was that he thought it was a mistake.

 

Climate time capsule from little ice age

The deep Pacific is a climate time capsule from the ‘little ice age,’ 19th century ship records show

By Paul Voosen |

NEW ORLEANS, LOUISIANA—A global cooling trend known as the “little ice age” ended centuries ago, but it lives on in the deepest parts of the Pacific Ocean, researchers reported here last week at a meeting of the American Geophysical Union. What’s more, this oceanographic time capsule could be helping blunt some of today’s human-driven warming, at least for now.

The oceans are a massive heat reservoir, absorbing some 90% of the warming from human-caused climate change. But this modern heat doesn’t penetrate evenly—or quickly—into their vast depths. As part of a network of global ocean currents called the thermohaline circulation, chilled surface waters in the North Atlantic Ocean dive into the deep and, over the course of many centuries, wind their way to the deep North Pacific, which is in many ways Earth’s cold storage locker.

That means the deep waters of the Pacific, unlike the relatively young Atlantic depths, should reflect surface temperature trends that are hundreds of years old. “From 1350 to the present day [those depths are] expected to be cooling,” says Jake Gebbie, a physical oceanographer at the Woods Hole Oceanographic Institution in Massachusetts, who presented the work. “Cooling—despite the fact that the surface is warming.”

A host of models of reconstructed global surface temperatures show that centuries ago, the world was unusually cold—as paintings of the frozen Thames River attest. After the “medieval warm period” ended in the 1400s, a cooling trend of a few tenths of a degree set in, ending only when human-driven warming began in the 1800s. By priming an ocean model with these historical surface temperatures, Gebbie and his co-author, Peter Huybers, a climate scientist at Harvard University, were able to predict where in the depths these trends would reveal themselves.

To test their model, they needed evidence of long-term temperature change from the deep ocean. But records below 2000 meters are sparse, produced only every decade or so during research cruises. And they’re seemingly nonexistent prior to the 20th century. But not entirely.

In the 1870s, a British research ship, the HMS Challenger, spent half a decade recording ocean temperatures during a grand scientific tour across the globe, making 760 readings below 2000 meters with thermometers lowered by rope. The duo compared the Challenger’s readings to measures taken from the 1970s onward, and tried to account for potential biases from that era, such as the stretchiness of hemp ropes and the behavior of early mercury thermometers under extreme pressure. After calibrating the old and modern data, “We see exactly what we see in the simulation,” Gebbie said, “deep Pacific cooling and deep Atlantic warming.”

In effect, the deep ocean acts as a filter, one that wipes out short-term temperature fluctuations and keeps the long-term trend. And this signal seems to persist despite large-scale phenomena, such as eddies, that can mix up the oceans. Assuming Gebbie’s model is correct, the deep Pacific will continue to cool for decades as the little ice age water arrives.

“This is fantastic,” says Yair Rosenthal, a paleoceanographer at Rutgers University in New Brunswick, New Jersey, who is impressed that Gebbie could trace the cooling flow of little ice age water to the deep Pacific. “If you caught a fish today in the deep Pacific and asked it what it thought about global warming,” Rosenthal says, “it’d think that we are talking about the medieval climate.”

But Greg Johnson, an oceanographer at the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory in Seattle, Washington, cautions that the researchers used a coarse model of the ocean, which may not adequately simulate real conditions. They also did not consider how decadeslong variations in North Atlantic currents could influence the trends they see. “It is an interesting result, but I am skeptical,” says Johnson, who is developing a program to regularly sample deep ocean temperatures with deep-diving robotic floats.

If real, this slow drop in deep ocean temperatures is a boon to a warming planet. If the little ice age hadn’t cooled the oceans, they’d likely be absorbing less heat from the atmosphere today, and surface warming would be much worse than it already is. “It’s buying us time,” Rosenthal says. “It’s buying us time.”

 

Radar images of Phaethon

Arecibo telescope captures images of near-Earth asteroid

After suffering structural damage during Hurricane Maria, Puerto Rico’s Arecibo Observatory is back online and monitoring the potentially hazardous near-Earth asteroid 3200 Phaethon, NASA’s Jet Propulsion Laboratory reports. The radar’s images reveal the ball-shaped asteroid is larger than previously estimated, coming in at about 6 kilometers wide, and about 10 times larger than asteriod Bennu, the target of NASA’s OSIRIS-REx spacecraft, Newsweek reports. The Arecibo Observatory, which has the world’s most powerful radar system, captured the images when Phaethon swung about 10 million kilometers from Earth or about 27 times the distance between Earth and the moon. That’s the closest the asteroid will get until 2093, researchers estimate, meaning Phaethon is unlikely to come in contact with Earth.

 

Primordial Black Holes

Primordial Black Holes and Cosmological Problems

ABSTRACT: It is argued that the bulk of black holes (BH) in the universe are primordial (PBH). This assertion is strongly supported by the recent astronomical observations, which allow to conclude that supermassive BHs with M= (106 – 109) M “work” as seeds for galaxy formation, intermediate mass BHs, M = (103 – 104) M, do the same job for globular clusters and dwarf galaxies, while black holes of a few solar masses are the constituents of dark matter of the universe. The mechanism of PBH formation, suggested in 1993, which predicted such features of the universe, is described. The model leads to the log-normal mass spectrum of PBHs, which is determined by three constant parameters. With proper adjustment of these parameters the above mentioned features are quantitatively explained. In particular, the calculated density of numerous superheavy BHs in the young universe, z = 5 – 10, nicely fits the data. The puzzling properties of the sources of the LIGO-discovered gravitational waves are also naturally explained assuming that these sources are PBHs.

 

Jets of AGN as co-axial cables

The Jets of AGN as giant co-axial cables

ABSTRACT: The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic (B) field, which will give rise to a systematic change in the RM across the jet. The aim of this study is to identify new AGNs displaying statistically significant transverse RM gradients across their parsec-scale jets, and to look for overall patterns in the implied directions for the toroidal B-field components and jet currents. We have carried out new analyses of Faraday RM maps derived from previously published 8.1, 8.4, 12.1 and 15.3 GHz data obtained in 2006 on the NRAO VLBA. In a number of important ways, our procedures were identical to those of the original authors, but several other key aspects of the new imaging and analysis differ from the original methods. Our new analysis has substantially increased the number of AGNs known to display transverse RM gradients. The collected data on parsec and kiloparsec scales indicate that the current typically flows inward along the jet axis and outward in a more extended region surrounding the jet, typical to the current structure of a coaxial cable, accompanied by a self-consistent system of nested helical B fields, whose toroidal components give rise to the observed transverse RM gradients. These new results make it possible for the first time to conclusively demonstrate the existence of a preferred direction for the toroidal B-field components – and therefore of the currents – of AGN jets. Discerning the origin of this current-field system is of cardinal importance for understanding the physical mechanisms leading to the formation of the intrinsic jet B field, which likely plays an important role in the propagation and collimation of the jets; one possibility is the action of a “cosmic battery”.

 

The Elusive Origin of Mercury

The Elusive Origin of Mercury

ABSTRACT: The MESSENGER mission sought to discover what physical processes determined Mercury’s high metal to silicate ratio. Instead, the mission has discovered multiple anomalous characteristics about our innermost planet. The lack of FeO and the reduced oxidation state of Mercury’s crust and mantle are more extreme than nearly all other known materials in the solar system. In contrast, moderately volatile elements are present in abundances comparable to the other terrestrial planets. No single process during Mercury’s formation is able to explain all of these observations. Here, we review the current ideas for the origin of Mercury’s unique features. Gaps in understanding the innermost regions of the solar nebula limit testing different hypotheses. Even so, all proposed models are incomplete and need further development in order to unravel Mercury’s remaining secrets.

 

Mars: Not as dry as it seems

Mars: Not as dry as it seems

When searching for life, scientists first look for an element key to sustaining it: fresh water.

Although today’s Martian surface is barren, frozen and inhabitable, a trail of evidence points to a once warmer, wetter planet, where water flowed freely. The conundrum of what happened to this water is long standing and unsolved. However, new research published in Nature suggests that this water is now locked in the Martian rocks.

Scientists at Oxford’s Department of Earth Sciences, propose that the Martian surface reacted with the water and then absorbed it, increasing the rocks oxidation in the process, making the planet uninhabitable.

Previous research has suggested that the majority of the water was lost to space as a result of the collapse of the planet’s magnetic field, when it was either swept away by high intensity solar winds or locked up as sub-surface ice. However, these theories do not explain where all of the water has gone.

Convinced that the planet’s minerology held the answer to this puzzling question, a team led by Dr Jon Wade, NERC Research Fellow in Oxford’s Department of Earth Sciences, applied modelling methods used to understand the composition of Earth rocks to calculate how much water could be removed from the Martian surface through reactions with rock. The team assessed the role that rock temperature, sub-surface pressure and general Martian make-up, have on the planetary surfaces.

The results revealed that the basalt rocks on Mars can hold approximately 25 per cent more water than those on Earth, and as a result drew the water from the Martian surface into its interior.

Dr Wade said: ‘People have thought about this question for a long time, but never tested the theory of the water being absorbed as a result of simple rock reactions. There are pockets of evidence that together, leads us to believe that a different reaction is needed to oxidise the Martian mantle. For instance, Martian meteorites are chemically reduced compared to the surface rocks, and compositionally look very different. One reason for this, and why Mars lost all of its water, could be in its minerology.

‘The Earth’s current system of plate tectonics prevents drastic changes in surface water levels, with wet rocks efficiently dehydrating before they enter the Earth’s relatively dry mantle. But neither early Earth nor Mars had this system of recycling water. On Mars, (water reacting with the freshly erupted lavas’ that form its basaltic crust, resulted in a sponge-like effect. The planet’s water then reacted with the rocks to form a variety of water bearing minerals. This water-rock reaction changed the rock mineralogy and caused the planetary surface to dry and become inhospitable to life.’

As to the question of why Earth has never experienced these changes, he said: ‘Mars is much smaller than Earth, with a different temperature profile and higher iron content of its silicate mantle. These are only subtle distinctions but they cause significant effects that, over time, add up. They made the surface of Mars more prone to reaction with surface water and able to form minerals that contain water. Because of these factors the planet’s geological chemistry naturally drags water down into the mantle, whereas on early Earth hydrated rocks tended to float until they dehydrate.’

The overarching message of Dr Wade’s paper, that planetary composition sets the tone for future habitability, is echoed in new research also published in Nature, examining the Earth’s salt levels. Co-written by Professor Chris Ballentine of Oxford’s Department of Earth Sciences, the research reveals that for life to form and be sustainable, the Earth’s halogen levels (Chlorine, Bromine and Iodine) have to be just right. Too much or too little could cause sterilisation. Previous studies have suggested that halogen level estimates in meteorites were too high. Compared to samples of the meteorites that formed the Earth, the ratio of salt to Earth is just too high.

Many theories have been put forward to explain the mystery of how this variation occurred, however, the two studies combined elevate the evidence and support a case for further investigation. Dr Wade said ‘Broadly speaking the inner planets in the solar system have similar composition, but subtle differences can cause dramatic differences — for example, rock chemistry. The biggest difference being, that Mars has more iron in its mantle rocks, as the planet formed under marginally more oxidising conditions.’

We know that Mars once had water, and the potential to sustain life, but by comparison little is known about the other planets, and the team are keen to change that.

Dr Wade, said: ‘To build on this work we want to test the effects of other sensitivities across the planets — very little is known about Venus for example. Questions like: what if the Earth had more or less iron in the mantle, how would that change the environment? What if the Earth was bigger or smaller? These answers will help us to understand how much of a role rock chemistry determines a planet’s future fate.

When looking for life on other planets it is not just about having the right bulk chemistry, but also very subtle things like the way the planet is put together, which may have big effects on whether water stays on the surface. These effects and their implications for other planets have not really been explored.’

Story Source:

Materials provided by University of Oxford. Note: Content may be edited for style and length.

 

Karen Jean Meech

Karen Jean Meech

Karen J. Meech (born 1959) is an American astronomer at the Institute for Astronomy in the University of Hawaii.

She specializes in planetary astronomy, in particular the study of distant comets and their relation to the early solar system. Meech is also very active in professional-amateur collaboration and science teacher education and was the founder of the Towards Planetary Systems (TOPS) high-school teacher / student outreach program that helps educate science teachers in the Pacific islands. She received her Ph.D. in Planetary Sciences in 1987 at the Massachusetts Institute of Technology, and a B.S. from Rice University in Houston in 1981, and has received several awards in her career, including the Annie J. Cannon Award in Astronomy in 1988 and the American Astronomical Society‘s H. C. Urey Prize in 1994.

She was a co-investigator on the Deep Impact mission and current co-investigator on the NASA Discovery missions EPOXI and Stardust-NExT. For all three of these missions she has coordinated the world’s Earth-based and space-based observing programs. She is the PI of the University of Hawaii NASA Astrobiology Institute lead team which focuses its research on “Water and Habitable Worlds”. She is currently the President of the International Astronomical Union Division III (Planetary Systems Science).

The outer main-belt asteroid 4367 Meech, discovered by Schelte Bus at the Siding Spring Observatory in 1981, is named in her honor.

 

Oumuamua: Red and extremely elongated

A brief visit from a red and extremely elongated interstellar asteroid

Nature 552, 378–381 (21 December 2017)

Karen J. Meech et al.

Abstract

None of the approximately 750,000 known asteroids and comets in the Solar System is thought to have originated outside it, despite models of the formation of planetary systems suggesting that orbital migration of giant planets ejects a large fraction of the original planetesimals into interstellar space. The high predicted number density of icy interstellar objects (2.4 × 10−4 per cubic astronomical unit) suggests that some should have been detected, yet hitherto none has been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of the Solar System today, but there has been no way of telling whether the Solar System is typical of planetary systems. Here we report observations and analysis of the object 1I/2017 U1 (‘Oumuamua) that demonstrate its extrasolar trajectory, and that thus enable comparisons to be made between material from another planetary system and from our own. Our observations during the brief visit by the object to the inner Solar System reveal it to be asteroidal, with no hint of cometary activity despite an approach within 0.25 astronomical units of the Sun. Spectroscopic measurements show that the surface of the object is spectrally red, consistent with comets or organic-rich asteroids that reside within the Solar System. Light-curve observations indicate that the object has an extremely oblong shape, with a length about ten times its width, and a mean radius of about 102 metres assuming an albedo of 0.04. No known objects in the Solar System have such extreme dimensions. The presence of ‘Oumuamua in the Solar System suggests that previous estimates of the number density of interstellar objects, based on the assumption that all such objects were cometary, were pessimistically low. Planned upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to result in the detection of more interstellar objects in the coming years.

 

`Oumuamua: Red, Tumbling, and Silent

`Oumuamua: Red, Tumbling, and Silent

Back in late October, in the days following the discovery of what proved to be an object from interstellar space, astronomers scrapped the observing plans at observatories worldwide to scrutinize this unique visitor before it zipped out of the inner solar system, never to return. Right now ‘Oumuamua (or 1I/2017 U1), as it’s now known, is some 350 million km (2.3 astronomical units) from Earth, has dimmed to only 27th magnitude, and is receding at another 5½ million km (15 Earth-Moon distances) each day.

But the flurry of observations made weeks ago, when it was closer and brighter, have fueled a second flurry of activity — writing scientific papers — to detail what we’ve learned. Here are three highlights that have come to light since S&T‘s previous update.

It’s Reddish

Some of the first observations of 1I/2017 U1 showed that it had a slightly reddish color, not unlike a class of red-tinged bodies (called D types) found in the outer asteroid belt. Careful spectral measurements made by Alan Fitzsimmons (Queens University Belfast) and others using the 4.2-m William Herschel Telescope and the 8.2-m Very Large Telescope bear out this initial assessment.

Writing in December 18th’s Nature Astronomy, the observers note that they don’t see any spectral evidence for outcrops of rocky minerals. This suggests that all of `Oumuamua might be covered with a veneer of icy organic compounds that have turned red after prolonged exposure to space radiation. This conversion doesn’t take very long on cosmic time-scales — roughly 10 million years — and for all we know this body had been drifting through interstellar space for billions of years before showing up on the Sun’s doorstep.

In fact, the Fitzsimmons team contends, the dark, reddish exterior of ‘Oumuamua might be masking an icy interior deeper down. The researchers calculate that the surface temperature soared to roughly 600 Kelvin during its brief but close encounter with the Sun (just 0.25 astronomical unit, well inside Mercury’s orbit). But they also find that a topside layer of irradiated, carbon-rich goo would only need to be a half meter thick to keep the Sun’s heat from reaching deeply buried water ice and even frozen carbon dioxide. They’d remain as ices, instead of sublimating and escaping in comet-like fashion.

“We recognize one obvious problem with this model,” the authors admit. Comets in our own Oort Cloud should likewise have built up thick mantles due to 4½ billion years of exposure to cosmic rays, yet most are clearly give off lots of gas as they near the Sun. One possible out: Maybe ‘Oumuamua spent enough time near its host star that become completely devolatilized before heading our way.

It’s Tumbling

It didn’t take observers long to realize that ‘Oumuamua displayed wild swings in brightness of up to 2½ magnitudes — a factor of 10! — that defied easy explanation. Surely it must be highly elongated, with a length 5 to 10 times its width (depending on whom you ask). Some of the initial reports suggesting a spin period of 7.5 hours proved premature.

A team led by Michal Drahus and Piotr Guzik (Jagiellonian University, Poland) used the Gemini North telescope to bag hundreds of images on October 27th and 28th. “While the light curve of 1I/‘Oumuamua is clearly periodic, it does not repeat exactly from one rotation cycle to another,” they write in an online preprint. “Furthermore, the light curve does not appear to have a single, unique periodicity because the rotation periods reported by other studies differ from one another and are inconsistent with our data.”

The object could only be spinning this erratically if it were tumbling, a characteristic that’s rare among our solar system’s asteroids and comets. (Comet 1P/Halley is a tumbler, for example, driven by assorted gas jets from its nucleus.) But ‘Oumuamua shows no hint of outgassing, and the chance that it struck something in our solar system en route to its discovery seems impossibly remote. Most likely, they conclude, it had a rough time while escaping from the system of its origin.

It’s Not Broadcasting!

One of the most unexpected studies occurred earlier this month when Breakthrough Listen — the initiative to find signs of intelligent life in the universe — funded an effort to eavesdrop on any radio transmissions that ‘Oumuamua might be broadcasting. On December 13th astronomers used the huge Robert C. Byrd Green Bank Telescope in West Virginia to listen to billions of radio frequences in four bands spanning 1 to 12 gigahertz.

The Green Bank search didn’t turn up any radio “beacons” or other transmissions in narrow frequency bands, though the analysis of three of the bands isn’t complete. Honestly, the Breakthrough Listen team didn’t expect to pick up alien broadcasts from this interloper — but, hey, why not try, right?

One final set of observations of 1I/2017 U1 is under way. Karen Meech and others are attempting to record images with the Hubble Space Telescope. Their aim is simply to locate its position against background stars as accurately as possible. Those measurements, in turn, will fine-tune calculations of the object’s in-bound trajectory and help us identify where this strange object came from and perhaps shed some light on how it got here.