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New Map of Dark Matter

Posted on July 17, 2021 by WykenSeagraveJuly 17, 2021

Dark matter is postulated to exist in order to explain the gravitational force which holds galaxies together. There is not enough visible matter to explain it.

Members of the international Dark Energy Survey (DES) team – a collaborative effort to reveal the nature of the mysterious dark energy that is driving the expansion of our universe – have created a map that covers a quarter of the sky of the southern hemisphere (an eighth of the total night sky visible from Earth).

The team used an international supercomputer to analyse images of 100 million galaxies, looking at their shape to see if the light had been stretched. This is one way to investigate dark matter.

If the light from distant galaxies has been distorted, it suggests there is matter in the way, bending the light as it comes towards us. Astronomers are mapping these distortions which may suggest invisible, but gravitating, mass.

More information

UK Research and Innovation website

Guardian report

The Late Devonian Extinction

Posted on July 17, 2021 by WykenSeagraveJuly 17, 2021

In a BBC Podcast first broadcast on 11 March 2021, Melvyn Bragg and guests discuss the devastating mass extinctions of the Late Devonian Period, roughly 370 million years ago, when around 70 percent of species disappeared.

Scientists are still trying to establish exactly what happened, when and why, but this was not as sudden as when an asteroid hits Earth. The Devonian Period had seen the first trees and soils and it had such a diversity of sea life that it’s known as the Age of Fishes, some of them massive and armoured, and, in one of the iconic stages in evolution, some of them moving onto land for the first time. One of the most important theories for the first stage of this extinction is that the new soils washed into oceans, leading to algal blooms that left the waters without oxygen and suffocated the marine life.

Listen here

Expanding Worldviews: Astrobiology, Big History and Cosmic Perspectives

Posted on August 19, 2019 by WykenSeagraveAugust 19, 2019

This conference, organised by Birkbeck Institute for the Humanities, will be held in London on 19 and 20 September 2019.

Astrobiology and Big History are two relatively new intellectual disciplines, the former focussed on searching for life elsewhere in the universe and the latter on integrating human history into the wider history of the cosmos. Despite some differences in emphasis these two disciplines share much in common, not least their interdisciplinarity and the cosmic and evolutionary perspectives that they both engender.

This meeting is held under the auspices of the Birkbeck Institute for the Humanities, the UCL/Birkbeck Centre for Planetary Sciences and the Birkbeck Centre for Legal Futures (formerly the Centre for Critical Study of European Law). It will provide a forum for discussing the relationships between Astrobiology and Big History, with an emphasis on their wider intellectual and societal benefits. It will build on an earlier meeting, Expanding Worldviews I, that was held at the Australian National University in July 2018 (a summary of which can be found here).

Confirmed speakers include:Stephen Baxter (SF author): ‘The visibility of big history’; Andreas Bummel (Democracy without Borders): ‘The political implications of a planetary worldview’; Klara Capova (European Space Agency): Title TBC; Lewis Dartnell (Westminster University): ‘How the world made us’; David Dunér (Lund University): ‘Extraterrestrial life and the human mind’; Caroline Edwards (Birkbeck): ‘From clean energy to climate change: Early martian literary utopias, 1877-1964’; Olivia Judson (Imperial College London/Freie Universität Berlin): Title TBC; Tony Milligan (King’s College, London): ‘Astrobiology and the outer limits of human ethics’; Annahita Nezami: ‘The psychology of the “Overview Effect” – What lies beneath?’; Esther Quaedackers (University of Amsterdam): ‘How understanding the emergence of life and human culture can help us understand the development of AI’

This event is free to attend, book via Eventbrite here

You can download the provisional programme here

Great Oxygen Poisoning

Posted on March 26, 2018 by WykenSeagraveMarch 26, 2018

About 2.4 billion years ago there was a dramatic increase in the level of free oxygen in the Earth’s atmosphere, which led to the widespread extinction of many species of bacteria which had evolved when the atmosphere was anaerobic. Previously it has been thought that this oxygen was released by blue-green bacteria, but in an article entitled “Large oxygen excess in the primitive mantle could be the source of the Great Oxygenation Event” published in January 2018, D. Andrault et al state that:

Before the Archean to Proterozoic Transition (APT) the tectonic regime was dominated by microplates floating on a low viscosity mantle. Such a regime restricted chemical exchange between the shallow and deeper mantle reservoirs. After the APT, a more global convection regime led to deep subduction of slabs.

They go on to propose that:

the improved vertical mixing of the mantle favoured the release to the Earth’s surface of an oxygen excess initially trapped in the deep mantle. This excess built up when the primordial lower mantle was left with a high Fe3+/(Fe2++Fe3+) ratio (#Fe3+), after metallic iron segregated down into the core. Our synchrotron-based in situ experiments suggest a primordial Fe3+excess of ~20 % for the mantle iron. By comparison with the #Fe3+ of the present mantle, this Fe3+excess would correspond to 500–1000 times the O2 content in the Earth’s atmosphere. The tectonic transition greatly facilitated the ascent of oxidised lower mantle material towards the Earth’s surface, inducing a continuous arrival of O2 at the Earth’s surface and into the atmosphere.

In other words, the oxygen was released when the previously floating plates began to be subducted into the mantle, creating convection currents which brought oxygen-rich rocks to the surface, where the oxygen was released.

But the date when subduction began is controversial. As S. Turner noted in his article “Heading down early on? Start of subduction on Earth” published in 2014:

Many workers suggest that subduction may have only commenced toward the end of the Archean or later [but] some form of subduction may have been operating as early as the Hadean or Eoarchean.

Redshift z value

Posted on December 16, 2016 by WykenSeagraveDecember 16, 2016

Redshift is the name given to the change in colour of objects which are moving away from us. At normal speeds this change is so small we do not notice, but when we use powerful telescopes to look at distant galaxies the colour change is measurable.

The cause of redshift is that light is a wave, and when the source of light moves away these waves are stretched out to a longer wavelength and so change colour towards the red end of the optical spectrum. Likewise, when objects move towards us their light waves are compressed and they look bluer than stationary objects.

We observe a similar phenomenon in our everyday lives when a vehicle passes us and we hear the sound of its engine drop as its sound waves change from being compressed (higher pitch) to stretched out (lower pitch). In this case the effect is called the “Doppler shift”

Astronomers use a value called z to measure the redshift of distant objects. It is calculated as the fractional change of wavelength of the moving object relative to a stationary object. Redshifts have positive values, blueshifts have negative ones and the z value of a stationary object is zero. The larger the z number, the faster it is moving.

Evolution of Milky Way-like Galaxies

Posted on November 16, 2016 by WykenSeagraveDecember 16, 2016

The images below show how galaxies similar in mass to our home galaxy, the Milky Way, evolved over time. The images taken by the NASA/ESA Hubble Space Telescope reveal that Milky Way-like galaxies grow larger in size and in stellar mass over billions of years. These images are part of the most comprehensive multi-observatory galaxy surveys yet. Stretching back in time more than 10 billion years, the census contains nearly 2 000 snapshots of Milky Way-like galaxies.

The images were taken between 2010 and 2012 with Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS).

For an explanation of the z values quoted below, see this Redshift article.

11.3 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 11.3 billion years ago. Z=2.8

The image above reveals a compact, youthful galaxy as it looked 11.3 billion years ago, when our Universe was only about 2.5 billion years old. The bluish-white glow reveals that the fledgling galaxy is undergoing a wave of star birth, as its rich reservoir of gas compresses under gravity, creating myriad stars.

10.9 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 10.9 billion years ago. z=2.4

10.3 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 10.3 billion years ago. z=2.0

At 10.3 billion years ago, the firestorm of star birth is reaching its peak. The stellar “baby boom” churned out stars 30 times faster than the Milky Way does today. The galaxy’s yellowish colour most likely highlights ongoing star formation that is being obscured by dust and gas.

8.9 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 8.9 billion years ago. z=1.3

Eventually, the galaxies exhaust their star-making gas. The galaxy at 8.9 billion years ago (image above) has developed a spiral shape, and the oldest stars reside in its central region.

6.1 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 6.1 billion years ago. z=0.65

By 6.3 billion years ago this similar galaxy had grown even larger. The galaxy was dominated by mostly older stars, which can be seen in its reddish appearance.

3.1 Billion Years Ago

This image, taken by the NASA/ESA Hubble Space Telescope, shows a galaxy similar in mass to the Milky Way. The galaxy is seen as it was 3.1 billion years ago. z=0.26

At 3,1 billion years ago this galaxy had clearly visible spiral arms dotted with clouds of gas lit by newly formed open star clusters.

References

NASA Composite Image

Reconstruction of 10 billion year old Milky Way

Reconstruction of Early Milky Way

Posted on November 15, 2016 by WykenSeagraveNovember 16, 2016

In one of the most comprehensive multi-observatory galaxy surveys yet, astronomers find that galaxies like our Milky Way underwent a stellar “baby boom,” churning out stars at a prodigious rate, about 30 times faster than today.

This illustration depicts a view of the night sky from a hypothetical planet within the youthful Milky Way galaxy 10 billion years ago. The heavens are ablaze with a firestorm of star birth. Glowing pink clouds of hydrogen gas harbor countless newborn stars, and the bluish-white hue of young star clusters litter the landscape. The star-birth rate is 30 times higher than it is in the Milky Way today. Our Sun, however, is not among these fledgling stars. The Sun will not be born for another 5 billion years.

Our Sun, however, is a late “boomer.” The Milky Way’s star-birthing frenzy peaked 10 billion years ago, but our Sun was late for the party, not forming until roughly 5 billion years ago. By that time the star formation rate in our galaxy had plunged to a trickle…

Source: Hubblesite.org

Astronomers don’t have baby pictures of our Milky Way’s formative years to trace the history of stellar growth. Instead, they compiled the story from studying galaxies similar in mass to our Milky Way, found in deep surveys of the universe. The farther into the universe astronomers look, the further back in time they are seeing, because starlight from long ago is just arriving at Earth now. From those surveys, stretching back in time more than 10 billion years, researchers assembled an album of images containing nearly 2,000 snapshots of Milky Way-like galaxies.

References

NASA News Release Nov 2015

Reconstruction Images

Evolution of galaxies similar to Milky Way

Universe has lost 90% of its galaxies

Posted on November 10, 2016 by WykenSeagraveNovember 10, 2016

In analyzing data from deep-sky census assembled from surveys taken by NASA’s Hubble Space Telescope and other observatories, a team led by Christopher Conselice of the University of Nottingham, U.K., found that 10 times as many galaxies were packed into a given volume of space in the early universe than found today.

Most of these galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way. As they merged to form larger galaxies the population density of galaxies in space dwindled. This means that galaxies are not evenly distributed throughout the universe’s history, the research team reports in a paper to be published in The Astrophysical Journal.

Reference

http://www.nasa.gov/feature/goddard/2016/hubble-reveals-observable-universe-contains-10-times-more-galaxies-than-previously-thought

Solar System is in Orion Arm of Galaxy

Posted on November 10, 2016 by WykenSeagraveNovember 10, 2016

The Orion Arm is a minor spiral arm of the Milky Way some 3,500 light-years (1,100 parsecs) across and approximately 10,000 light-years (3,100 parsecs) in length. The Solar System, including the Earth, lies within the Orion Arm. It is also referred to by its full name, the Orion–Cygnus Arm, as well as Local Arm, Orion Bridge, and formerly, the Local Spur and Orion Spur.

References

https://en.wikipedia.org/wiki/Orion_Arm?wprov=sfla1

Earth’s magnetic field maintained by Moon

Posted on April 28, 2016 by WykenSeagraveApril 28, 2016

The Earth’s magnetic field permanently protects us from the charged particles and radiation that originate in the Sun. This shield is produced by the geodynamo, the rapid motion of huge quantities of liquid iron alloy in the Earth’s outer core. To maintain this magnetic field until the present day, the classical model required the Earth’s core to have cooled by around 3 000 °C over the past 4.3 billion years. Now, a team of researchers from CNRS and Université Blaise Pascal, Clermont-Ferrand, France, suggests that, on the contrary, its temperature has fallen by only 300 °C. The action of the Moon, overlooked until now, is thought to have compensated for this difference and kept the geodynamo active. Their work is published on 30 march 2016 in the journal Earth and Planetary Science Letters.

More information from

http://www2.cnrs.fr/en/2735.htm