helium Archives

December 2, 2013March 14, 2017 by Fraser Cain

How Does a Star Form?

We owe our entire existence to the Sun. Well, it and the other stars that came before. As they died, they donated the heavier elements we need for life. But how did they form?

Stars begin as vast clouds of cold molecular hydrogen and helium left over from the Big Bang. These vast clouds can be hundreds of light years across and contain the raw material for thousands or even millions of times the mass of our Sun. In addition to the hydrogen, these clouds are seeded with heavier elements from the stars that lived and died long ago. They’re held in balance between their inward force of gravity and the outward pressure of the molecules. Eventually some kick overcomes this balance and causes the cloud to begin collapsing.

That kick could come from a nearby supernova explosion, collision with another gas cloud, or the pressure wave of a galaxy’s spiral arms passing through the region. As this cloud collapses, it breaks into smaller and smaller clumps, until there are knots with roughly the mass of a star. As these regions heat up, they prevent further material from falling inward.

At the center of these clumps, the material begins to increase in heat and density. When the outward pressure balances against the force of gravity pulling it in, a protostar is formed. What happens next depends on the amount of material.

Some objects don’t accumulate enough mass for stellar ignition and become brown dwarfs – substellar objects not unlike a really big Jupiter, which slowly cool down over billions of years.

If a star has enough material, it can generate enough pressure and temperature at its core to begin deuterium fusion – a heavier isotope of hydrogen. This slows the collapse and prepares the star to enter the true main sequence phase. This is the stage that our own Sun is in, and begins when hydrogen fusion begins.

If a protostar contains the mass of our Sun, or less, it undergoes a proton-proton chain reaction to convert hydrogen to helium. But if the star has about 1.3 times the mass of the Sun, it undergoes a carbon-nitrogen-oxygen cycle to convert hydrogen to helium. How long this newly formed star will last depends on its mass and how quickly it consumes hydrogen. Small red dwarf stars can last hundreds of billions of years, while large supergiants can consume their hydrogen within a few million years and detonate as supernovae. But how do stars explode and seed their elements around the Universe? That’s another episode.

We have written many articles about star formation on Universe Today. Here’s an article about star formation in the Large Magellanic Cloud, and here’s another about star formation in NGC 3576.

Want more information on stars? Here’s Hubblesite’s News Releases about Stars, and more information from NASA’s imagine the Universe.

We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?

Source: NASA

June 7, 2011December 24, 2015 by Jason Major

A White-Hot Relationship

Artist's impression of white dwarf binary pair CSS 41177. Image: Andrew Taylor.

[/caption]

Two stars have been discovered locked in a mutually-destructive embrace, a relationship that will end with both losing their individual identities as they spiral increasingly closer, eventually becoming a single hot body that is destined to quickly fizzle out.

No, we’re not talking about the cover of a Hollywood tabloid, these are two white dwarf stars 1,140 light-years away in the constellation Leo, and they are the second such pair of their kind ever to be discovered.

Astronomers at the University of Warwick in the UK have identified a binary pair of white dwarf stars named CSS 41177 that circle each other closely in an eclipsing orbit. What’s particularly unique about this pair is that both stars seem to have been stripped down to their helium layers – a feature that points at an unusually destructive history for both.

White dwarfs typically form from larger stars that have burned through their hydrogen and helium, leaving behind hot, dense cores composed of carbon and oxygen – after going through a bloated red giant phase, that is. But when stars are very close to each other, such as in the case of binary pairs, the expanding hydrogen shell from the larger one undergoing its red giant phase is stripped away by its smaller companion, which absorbs the material. Without the compression and heat from the hydrogen layer the first star cannot fuse its helium into heavier elements and is left as a helium white dwarf.

When the time comes for the smaller star to expand into a red giant, its outer layers are likewise torn away by the first star. But the first star cannot use that hydrogen, and so both are left as helium white dwarfs. The unused hydrogen is ultimately lost to the system.

It’s a case of a destructive codependent relationship on a stellar scale.

The white dwarf stars in CSS 41177 will eventually merge together in about a billion years, gaining enough mass in the process to begin fusing their combined helium, thus becoming a single star called a hot subdwarf. This period could last another 100 million years.

This discovery was made using data gathered from the Liverpool Telescope in the Canary Islands and the Gemini Telescope on Hawaii. The paper was accepted for publication in the Astrophysical Journal and is entitled A deeply eclipsing detached double helium white dwarf binary. (Authors: S. G. Parsons, T. R. Marsh, B. T. Gaensicke, A. J. Drake, D. Koester.)

Where is Helium Found

[/caption]

Helium is the second lightest element in the known universe. It is also the second most abundant. According to some estimates helium accounts for as much as 24 percent of the Universe’s mass. This element is also plentiful since it is a prime product of fusion nuclear reactions involving hydrogen. So if it is so plentiful where is Helium found?

The problem is that just because an element is common in the universe at large does not mean that it is common on Earth. Helium is an element that fits this scenario. Helium only accounts for 0.00052% of the Earth’s atmosphere and the majority of the helium harvested comes from beneath the ground being extracted from minerals or tapped gas deposits. This makes it one of the rarest elements of any form on the planet.

Like mentioned before Helium is rare on Earth but there are places where it is readily found. If you look at space the majority of helium is in stars and the interstellar medium. This is due to the fusion reaction that powers most stars fusing single hydrogen atoms to create helium atoms. This process balanced with a star’s gravity is what helps it to stay stable for billions of years. On Earth the majority of helium found comes from radioactive decay. This is the opposite nuclear reaction called fission that splits atoms. For this reason radioactive minerals in the lithosphere like uranium are prime sources for helium.

On Earth there are key locations where concentrated helium can be harvested. The United States produces the majority of the world’s helium supply at 78%. The rest of the world’s helium is harvested in North Africa, The Middle East, and Russia. The interesting thing is that thanks to these deposits the world’s demand for helium is being met regularly. Also unlike petroleum which can decades to form from organic material, 3000 metric tons of Hydrogen is produced yearly. Until helium demand reaches at least the same level of demand as petroleum there it little chance of that demand outpacing supply.

Helium is looking to be a major player in the near future. Governments are looking into using the gas as source of hydrogen for fuel cells and other transportation technologies. At the moment the promise is still tentative but at least with better surveying and knowledge of gas deposits there will be a supply waiting if becomes the next major element to power human civilization. In the meanwhile ours is still a planet beholden to carbon.

We have written many articles about Helium for Universe Today. Here’s an article about the discovery of Helium, and here’s an article about composition of the Sun.

If you’d like more info about helium on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Source: Wikipedia