LUCY, THE WHITE DWARF STAR BPM 37093 DIAMOND

Today, The Grandma has received the wonderful visit of one of her closest friends, Joseph de Ca'th Lon. They have been talking about Lucy, the universe's largest known diamond white dwarf star BPM 37093 discovered by the Harvard–Smithsonian Center for Astrophysics on a day like today in 2004, and named like this after The Beatles' song Lucy in the Sky with Diamonds.

 

The Center for Astrophysics-Harvard & Smithsonian (CfA) is an astrophysics research institute jointly operated by the Harvard College Observatory and Smithsonian Astrophysical Observatory.

Founded in 1973 and headquartered in Cambridge, Massachusetts, the CfA leads a broad program of research in astronomy, astrophysics, Earth and space sciences, as well as science education. The CfA either leads or participates in the development and operations of more than fifteen ground and space-based astronomical research observatories across the electromagnetic spectrum, including the forthcoming Giant Magellan Telescope (GMT) and the Chandra X-ray Observatory, one of NASA's Great Observatories.

Hosting more than 850 scientists, engineers, and support staff, the CfA is among the largest astronomical research institutes in the world.

More information: CFA

Its projects have included Nobel Prize-winning advances in cosmology and high energy astrophysics, the discovery of many exoplanets, and the first image of a black hole. The CfA also serves a major role in the global astrophysics research community: the CfA's Astrophysics Data System (ADS), for example, has been universally adopted as the world's online database of astronomy and physics papers. Known for most of its history as the Harvard-Smithsonian Center for Astrophysics, the CfA rebranded in 2018 to its current name in an effort to reflect its unique status as a joint collaboration between Harvard University and the Smithsonian Institution.

A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth.

A white dwarf's faint luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910.  The name white dwarf was coined by Willem Luyten in 1922.

White dwarfs are thought to be the final evolutionary state of stars whose mass is not high enough to become a neutron star or black hole. This includes over 97% of the other stars in the Milky Way.

After the hydrogen-fusing period of a main-sequence star of low or medium mass ends, such a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process.

If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, around 1 billion K, an inert mass of carbon and oxygen will build up at its center.

After such a star sheds its outer layers and forms a planetary nebula, it will leave behind a core, which is the remnant white dwarf. Usually, white dwarfs are composed of carbon and oxygen (CO white dwarf). If the mass of the progenitor is between 8 and 10.5 solar masses (M☉), the core temperature will be sufficient to fuse carbon but not neon, in which case an oxygen-neon-magnesium (ONeMg or ONe) white dwarf may form. Stars of very low mass will be unable to fuse helium; hence, a helium white dwarf may form by mass loss in binary systems.

The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense.

The physics of degeneracy yields a maximum mass for a non-rotating white dwarf, the Chandrasekhar limit -approximately 1.44 times M☉- beyond which it cannot be supported by electron degeneracy pressure.

More information: BBC

A carbon-oxygen white dwarf that approaches this mass limit, typically by mass transfer from a companion star, may explode as a type Ia supernova via a process known as carbon detonation; SN 1006 is thought to be a famous example.

A white dwarf is very hot when it forms, but because it has no source of energy, it will gradually cool as it radiates its energy away. This means that its radiation, which initially has a high color temperature, will lessen and redden with time. Over a very long time, a white dwarf will cool and its material will begin to crystallize, starting with the core.

The star's low temperature means it will no longer emit significant heat or light, and it will become a cold black dwarf. Because the length of time it takes for a white dwarf to reach this state is calculated to be longer than the current age of the known universe, approximately 13.8 billion years, it is thought that no black dwarfs yet exist.

The oldest known white dwarfs still radiate at temperatures of a few thousand kelvins, which establishes an observational limit on the maximum possible age of the universe.

BPM 37093 (V886 Centauri) is a variable white dwarf star of the DAV, or ZZ Ceti, type, with a hydrogen atmosphere and an unusually high mass of approximately 1.1 times the Sun's.

It is about 50 light-years from Earth, in the constellation Centaurus, and vibrates; these pulsations cause its luminosity to vary.

Like other white dwarfs, BPM 37093 is thought to be composed primarily of carbon and oxygen, which are created by thermonuclear fusion of helium nuclei in the triple-alpha process.

More information: Natural Diamonds

Picture yourself in a boat on a river
With tangerine trees and marmalade skies
Somebody calls you, you answer quite slowly
A girl with kaleidoscope eyes
Lucy in the sky with diamonds.

John Lennon & Paul Mccartney

LUCY: AUSTRALOPITHECUS AFARENSIS

Lucy

Australopithecus Afarensis is one of the best known of our ancestors due to a number of major discoveries including a set of fossil footprints and a fairly complete fossil skeleton of a female nicknamed 'Lucy'.This species lived between 3.9 and 2.8 million years ago. Australopithecus means ‘southern ape’ and was originally developed for a species found in South Africa. This is the genus or group name and several closely related species now share this name.

The word afarensis is based on the location where some of the first fossils for this species were discovered – the Afar Depression in Ethiopia, Africa.

During the 1970s, two fossil hunting teams began uncovering evidence of ancient human ancestors in east Africa. One team, co-led by Donald Johanson, was working at Hadar in Ethiopia. The other team led by Mary Leakey, was over 1,500 kilometres away at Laetoli in Tanzania. Fossils discovered at the two sites were found to have very similar features and ages but they did not match the fossils of any species known at that time. A new species name, Australopithecus afarensis, was therefore created for them in 1978.

More information: Lucy's Story by Institute of Human Origins

This species is now represented by several hundred fossils from east Africa like ‘Lucy’AL 288-1, Knee AL 129 1a + 1b, LH 4, The ‘First Family’, ‘Selam’ or ‘Lucy’s baby and ‘Lucy's big brother'.

Australopithecus afarensis is usually considered to be a direct ancestor of humans. It is also considered to be a direct ancestor of later species of Australopithecus and all species in the Paranthropus genus.

More information: Smithsonian Institution

The names Praeanthropus africanus and Praeanthropus afarensis have been suggested as alternatives by researchers who believe this species does not belong in the genus Australopithecus.

Fossils show this species was bipedal (able to walk on two legs) but still retained many ape-like features including adaptations for tree climbing, a small brain, and a long jaw.

This species probably used simple tools that may have included sticks and other non-durable plant materials found in the immediate surroundings. 

Stones may also have been used as tools, but there is no evidence that stones were shaped or modified in any way. 


It seems likely that they lived in small social groups containing a mixture of males and females, children and adults. Females were much smaller than males.

This species occupied a range of environments. Some populations lived in savannah or sparse woodland; others lived in denser forests beside lakes. Analysis of their teeth, skull and body shape indicates a diet that consisted mainly of plants. However, fossil animal bones with cut marks found in Dikika in 2010 have been attributed to this species, suggesting they may have included significant amounts of meat in their diets.

Microscopic analysis of their tooth enamel shows that they mostly ate fruits and leaves rather than seeds and other hard plant material. Their cone-shaped rib cage indicates they had large bellies adapted to a relatively low quality and high bulk diet. The position of the sagittal crest toward the back of the skull indicates that the front teeth processed most of the food.

More information: IPHES

If you were to go to the National Museum in Addis Ababa, you would walk into a huge room filled with literally tens of tons of fossils, and most of them would be elephants and rhinos and hippopotamus and monkeys and giraffes and antelopes and so on. Hominids are very rare in the landscape, and it's very rare to find them.

 Donald Johnson