Researchers find Earth composed of different materials than primitive meteorites

An independent compound chondrule consisting of barred olivine and porphyritic olivine section in the meteorite NWA 2372 CK4. Image courtesy of John Kashuba. Credit: Lawrence Livermore National Laboratory

Scientists from Lawrence Livermore National Laboratory (LLNL) have found that, contrary to popular belief, the Earth is not comprised of the same material found in primitive meteorites (also known as chondrites). 

This is based on the determination that the abundance of several neodymium (Nd) isotopes are different in the Earth and in chondritic meteorites.

A long-standing theory assumes that the chemical and isotopic composition of most elements in the bulk silicate Earth is the same as primitive meteorites.

However, 10 years ago it was discovered that rocks on the surface of the Earth had a higher abundance of 142Nd than primitive meteorites, leading to a hypothesis that Earth had either a hidden reservoir of Nd in its mantle or inherited more of the parent isotope 146smarium (Sm), which subsequently decayed to 142Nd.

Using higher precision isotope measurements, the team found that differences in 142Nd between Earth and chondrites (non-metallic meteorites) reflected nucleosynthetic processes and not the presence of a hidden reservoir in the Earth or excess 146Sm.

"The research has tremendous implications for our fundamental understanding of the Earth, not only for determining its bulk composition, heat content and structure, but also for constraining the modes and timescales of its geodynamical evolution," said Lars Borg, LLNL chemist and co-author of a paper appearing in the Sept. 15 edition of Nature .

The team suggests that the Earth formed from material that was slightly more enriched in Nd produced by the a slow neutron capture process during the creation of asymmetric giant branch (AGB) stars.

The team's ultimate goal was to determine whether the magnitude of radiogenic (produced by radioactive decay) Nd correlated with Nd produced in nucleosynthetic environments such as supernova or AGB stars.They used large sample sizes (about 2 grams) to obtain higher precision Nd and Sm isotope data for a comprehensive set of meteorites including 18 chondrites, the ungrouped primitive achondrite NWA 5363 and a Calcium-Aluminum-rich inclusion (CAI) from the Allende meteorite (the largest carbonaceous chondrite ever found on Earth).

"This research may provide a new means for assessing processes that affected solid material in the disk, as well as for identifying genetic relationships among planetary bodies," Borg said. "It calls into question a fundamental tenant of geochemistry that the composition of the Earth is precisely represented by the composition of primitive meteorites."

Other scientists include collaborators from the University of Chicago and Westfalische Wilhelms-Universitat Munster in Germany.

Neodymium is a powerful magnetic element used in compact electric motors. A Toyota Prius uses 1 kg in its electric motor magnets. Although neodymium is classifed as a rare earth element, it is fairly common, no rarer than cobalt, nickel and copper and is widely distributed in the Earth's crust. 

More information: C. Burkhardt et al. A nucleosynthetic origin for the Earth's anomalous 142Nd composition, Nature (2016). DOI: 10.1038/nature18956

Provided by: Lawrence Livermore National Laboratory

Find the Andromeda galaxy

in Clusters Nebulae Galaxies 

At 2.3 million light-years, the Andromeda galaxy is the closest spiral galaxy to our Milky Way and the most distant thing you can see with your eye alone.

The Andromeda Galaxy with two of its satellite galaxies, via Wikimedia Commons. Click here to expand.

 Although a couple of dozen minor galaxies lie closer to our Milky Way, the Andromeda galaxy is the closest major galaxy to ours. Excluding the Large and Small Magellanic Clouds, which can’t be seen from northerly latitudes, the Andromeda galaxy – also known as M31 – is the brightest galaxy in all the heavens. It’s the most distant thing you can see with your unaided eye, at 2.3 million light-years. To the eye, it appears as a smudge of light larger than a full moon. Follow the links below to learn more about the Andromeda galaxy.

Josh Blash captured this image of the Andromeda galaxy.

When to look for the Andromeda Galaxy. From mid-northern latitudes, you can see M31 – also called the Andromeda galaxy – for at least part of every night, all year long. But most people see the galaxy first in northern autumn, when it’s high enough in the sky to be seen from nightfall till daybreak. 

In late September and early October, the Andromeda galaxy shines in your eastern sky at nightfall, swings high overhead around midnight (1 a.m. daylight saving time) and stands rather high in the west at the onset of morning dawn. Winter evenings are also good for viewing the Andromeda galaxy.

If you are far from city lights, and it’s a moonless night – and you’re looking on an autumn or winter evening – it’s possible you’ll simply notice the galaxy in your night sky. It’s looks like a hazy patch in the sky, as wide across as a full moon.

But if you look, and don’t see the galaxy – yet you know you’re looking at a time when it’s above the horizon – you can star-hop to find the galaxy in one of two ways. First, you can use the Great Square of Pegasus. Second, you can use the constellation Cassiopeia.

Use the Great Square of Pegasus to find the Andromeda Galaxy. A line between Mirach and Mu Andromedae points to the galaxy.

 Find the Andromeda galaxy using the Great Square of Pegasus. You’ll be hopping to the Andromeda galaxy from the Great Square of Pegasus. In autumn, the Great Square of Pegasus looks like a great big baseball diamond in the eastern sky. Envision the bottom star of the Square’s four stars as home plate, then draw an imaginary line from the “first base” star though the “third base” star to locate two streamers of stars flying away from the Great Square. These stars belong to the constellation Andromeda the Princess.

On each streamer, go two stars north (left) of the third base star, locating the stars Mirach and Mu Andromedae. Draw a line from Mirach through Mu Andromedae, going twice the Mirach/Mu Andromedae distance. You’ve just landed on the Andromeda galaxy, which looks like a smudge of light to the unaided eye. 

If you can’t see the Andromeda galaxy with the eye alone, by all means use binoculars.

Many people use the M- or W-shaped constellation Cassiopeia to find the Andromeda galaxy. See how the star Schedar points to the galaxy?

Find the Andromeda galaxy using the constellation Cassiopeia. The constellation Cassiopeia the Queen is one of the easiest constellations to recognize. It is shaped like the letter M or W. Look generally northward on the sky’s dome to find this constellation. If you can recognize the north star, Polaris – and if you know how to find the Big Dipper – be aware that the Big Dipper and Cassiopeia move around Polaris like the hands of a clock, always opposite each other.

To find the Andromeda galaxy via Cassiopeia, look for the star Schedar. In the illustration above, see how the star Schedar points to the galaxy?

Many people use the Cassiopeia to find the Andromeda galaxy, because Cassiopeia itself is so easy to spot.

The Great Andromeda Nebula, photographed in the year 1900. At this point, astronomers could not discern individual stars in the galaxy. Many thought it was a cloud of gas within our Milky Way – a place where new stars were forming. Image via Wikimedia Commons.

History of our knowledge of the Andromeda galaxy. At one time, the Andromeda galaxy was called the Great Andromeda Nebula. Astronomers thought this patch of light was composed of glowing gases, or was perhaps a solar system in the process of formation. 

It wasn’t until the 20th century that astronomers were able to resolve the Andromeda spiral nebula into individual stars. This discovery lead to a controversy about whether the Andromeda spiral nebula and other spiral nebulae lie within or outside the Milky Way. 

In the 1920s Edwin Hubble finally put the matter to rest, when he used Cepheid variable stars within the Andromeda galaxy to determine that it is indeed an island universe residing beyond the bounds of our Milky Way galaxy.

Artist’s illustration of our Local Group via Chandra X-Ray Observatory.

 Andromeda and Milky Way in context. The Andromeda galaxy and our Milky Way galaxy reign as the two most massive and dominant galaxies within the Local Group of Galaxies. The Andromeda Galaxy is the largest galaxy of the Local Group, which, in addition to the Milky Way, also contains the Triangulum Galaxy, and about 30 other smaller galaxies. 

Both the Milky Way and the Andromeda galaxies lay claim to about a dozen satellite galaxies. Both are some 100,000 light-years across, containing enough mass to make billions of stars.

Astronomers have discovered that our Local Group is on the outskirts of a giant cluster of several thousand galaxies – which astronomers call the Virgo Cluster.

We also know of an irregular supercluster of galaxies, which contains the Virgo Cluster, which in turn contains our Local Group, which in turn contains our Milky Way galaxy and the nearby and Andromeda galaxy. At least 100 galaxy groups and clusters are located within this Virgo Supercluster. Its diameter is thought to be about 110 million light-years.

The Virgo Supercluster is thought to be one of millions of superclusters in the observable universe.

Earthsky friend Thomas Wildoner, caught the Andromeda galaxy in August 2014.

Bottom line: At 2.3 million light-years, the Great Andromeda galaxy (Messier 31) rates as one of the most distant objects you can see with the unaided eye. It is also the closest and brightest spiral galaxy to our Milky Way galaxy. This post tells how to find it, some of its history and gives some context for thinking about both our Milky Way galaxy and the Andromeda galaxy in the universe.

The Andromeda galaxy (M31) is at RA: 0h 42.7m; Dec: 41^o 16′ north

Starving black hole returns brilliant galaxy to the shadows

This image from the MUSE instrument on ESO’s Very Large Telescope shows the active galaxy Markarian 1018, which has a supermassive black hole at its core. The faint loops of light around the galaxy are a result of its interaction and merger with another galaxy in the recent past. Credit: ESO/CARS survey

The mystery of a rare change in the behaviour of a supermassive black hole at the centre of a distant galaxy has been solved by an international team of astronomers using ESO's Very Large Telescope along with the NASA/ESA Hubble Space Telescope and NASA's Chandra X-ray Observatory. It seems that the black hole has fallen on hard times and is no longer being fed enough fuel to make its surroundings shine. 

Many galaxies are found to have an extremely bright core powered by a supermassive black hole. These cores make "active galaxies" some of the brightest objects in the Universe. They are thought to shine so brightly because hot material is glowing fiercely as it falls into the black hole, a process known as accretion. This brilliant light can vary hugely between different active galaxies, so astronomers classify them into several types based on the properties of the light they emit.

Some of these galaxies have been observed to change dramatically over the course of only 10 years; a blink of an eye in astronomical terms. However, the active galaxy in this new study, Markarian 1018 stands out by having changed type a second time, reverting back to its initial classification within the last five years. A handful of galaxies have been observed to make this full-cycle change, but never before has one been studied in such detail.

The discovery of Markarian 1018's fickle nature was a chance by-product of the Close AGN Reference Survey (CARS), a collaborative project between ESO and other organisations to gather information on 40 nearby galaxies with active cores. Routine observations of Markarian 1018 with the Multi-Unit Spectroscopic Explorer (MUSE) installed on ESO's Very Large Telescope revealed the surprising change in the light output of the galaxy.

"We were stunned to see such a rare and dramatic change in Markarian 1018", said Rebecca McElroy, lead author of the discovery paper and a PhD student at the University of Sydney and the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO).

This sequence takes the viewer deep into the rather faint constellation of Cetus (The Sea Monster). In the final stages the faint active galaxy Markarian 1018 is seen, in a recent image from the MUSE instrument on ESO’s Very Large Telescope. Credit: ESO/A. Fujii/Digitized Sky Survey 2/CARS survey

The chance observation of the galaxy so soon after it began to fade was an unexpected opportunity to learn what makes these galaxies tick, as Bernd Husemann, CARS project leader and lead author of one of two papers associated with the discovery, explained: "We were lucky that we detected the event just 3-4 years after the decline started so we could begin monitoring campaigns to study details of the accretion physics of active galaxies that cannot be studied otherwise."

The research team made the most of this opportunity, making it their first priority to pinpoint the process causing Markarian 1018's brightness to change so wildly. This could have been caused by any one of a number of astrophysical events, but they could rule out the black hole pulling in and consuming a single star and cast doubt on the possibility of obscuration by intervening gas. But the true mechanism responsible for Markarian 1018's surprising variation remained a mystery after the first round of observations.

However, the team were able to gather extra data after they were awarded observing time to use the NASA/ESA Hubble Space Telescope, and NASA's Chandra X-ray Observatory. With the new data from this suite of instruments they were able to solve the mystery—the black hole was slowly fading because it was being starved of accretion material.

"It's possible that this starvation is because the inflow of fuel is being disrupted", said Rebecca McElroy. "An intriguing possibility is that this could be due to interactions with a second supermassive black hole". Such a black hole binary system is a distinct possibility in Markarian 1018, as the galaxy is the product of a major merger of two galaxies—each of which likely contained a supermassive black hole in its centre.

Research continues into the mechanisms at work in active galaxies such as Markarian 1018 that change their appearance. "The team had to work fast to determine what was causing Markarian 1018's return to the shadows," comments Bernd Husemann. "Ongoing monitoring campaigns with ESO telescopes and other facilities will allow us to explore the exciting world of starving black holes and changing active galaxies in more detail."

This research was presented in two papers entitled "Mrk 1018 returns to the shadows after 30 years as a Seyfert 1", and "What is causing Mrk 1018's return to the shadows after 30 years?", both to appear as Letters in the journal Astronomy & Astrophysics.