Featured Research

from universities, journals, and other organizations

New insight into atomic nuclei may explain how supernovas formed elements crucial to humankind

Date:
May 8, 2012
Source:
University of Oslo
Summary:
New insight into the behaviour of atomic nuclei may explain how gigantic star explosions, or supernovas, have formed the elements that are crucial to humankind.

Supernova explosion: Today astrophysicists are struggling to perform computer simulations of a supernova (a massive star explosion). New knowledge about atomic nuclei from the University of Oslo may make such simulations easier.
Credit: NASA

Ground-breaking research in nuclear physics at the University of Oslo may help astrophysicists understand how the heavier elements in our universe were made.

The Big Bang only produced the lightest elements, such as hydrogen and helium. One of the fundamental questions of astrophysics is how all the other elements were formed. In 1957, American researchers concluded that elements were formed through nuclear reactions inside stars.

Astrophysicists have believed that half the elements which are heavier than iron were formed in gigantic star explosions, known as supernovas.

However, there is one little snag with this theory: Astrophysicists have huge problems to make computer simulations of a supernova.

"A supernova is extremely complicated. Astrophysicists have not yet managed to make realistic computer simulations of supernova explosions," says nuclear physicist Ann-Cecilie Larsen at the SAFE-Centre for Accelerator-based Research and Energy Physics at the University of Oslo.

The simulations are based on certain characteristics of the atomic nucleus that are taken for granted but which have never been tested, as these characteristics are hard to determine.

Now, experiments carried out at the University of Oslo show that astrophysicists are using the wrong data in their models. No one has ever carried out these experiments before. The new results may have a great impact.

"Calculations show that it will be 200 to 300 times easier to achieve specific nuclear reactions in a supernova with our data," Larsen says to the research magazine Apollon at University of Oslo.

Stars with onion-like layers

In order to understand this discovery, we must take a few steps back.

"In earlier times we thought the Sun was fuelled by coal. However, when we came to understand how old the solar system actually was, we realized there wasn't enough coal to fuel the Sun. Instead, the production of heat was explained by fusion, in other words melting nuclei together."

The Sun consists of approximately 75 per cent hydrogen, 23 per cent helium and a small portion of heavier elements. Pairs of hydrogen atoms fuse into helium atoms when the temperature and the pressure are so high that they exceed the electromagnetic forces that push the atoms apart. This is what happens at the centre of the Sun, where temperatures reach 15 million degrees Celsius.

About four billion years from now, all the hydrogen will be burned up. The combustion of helium will start, converting helium into carbon and oxygen. When the helium is burned up, the combustion of carbon and oxygen starts. In this way, increasingly heavy elements are formed.

"Imagine the Sun as an onion with multiple layers. The heaviest element is formed at the core, whereas the outer layers have lighter elements."

When the Sun expires, the core of the Sun will be transformed into neon. In a really heavy star, the core will have turned into iron. Then it will be over. A dying star will never be able to form heavier elements than iron. And the explanation is surprisingly simple.

"Stars do not gain energy by burning heavier atomic nuclei. This has to do with the nuclear binding energy."

In nuclear physics, energy can be released by fusing small atomic nuclei. This process is called fusion.

When the elements are heavier than iron, it is only possible to extract energy from nuclear reactions by splitting the atomic nucleus. This process is called fission, which we know from nuclear power plants.

In order for a dying star to end up as a supernova, its core must have been transformed into iron.

"Once the core cannot be compressed any further, the compressed matter must expand again in a gigantic explosion, or supernova. This is where the heavy elements of the universe may have been formed."

Atomic collisions

Nuclear physicists at the University of Oslo have measured the energy states of the elements iron and molybdenum. The results of these experiments could change our understanding of supernova explosions. All the experiments were conducted in the cyclotron laboratory at UiO, where nuclear physicists can measure what happens when atomic nuclei collide with each other at very high speeds.

The protons and neutrons are put very tightly together and orbit inside the nucleus itself. Protons are positively charged particles. Neutrons are not charged.

In one of the experiments the nuclear physicists shoot at a target consisting of iron, with helium ions. When a huge amount of energy is given to the iron nuclei, the protons and neutrons of the iron core are pushed into a new orbit. In the second experiment, helium is shot at molybdenum.

"The atomic nuclei become highly excited and emit electromagnetic radiation. This radiation can be measured. The characteristics of the atomic nucleus appear to be different to what was previously thought."

Instead of releasing all the energy in a single quantum leap, the atomic nucleus releases energy in a series of small quantum leaps.

"Our experiments show a strong probability that the atomic nucleus releases small amounts of energy. It has been widely believed that this had little effect on the formation of elements in supernovae. We were surprised. The dynamics of the element production could be very different. All the atomic nuclei are connected in a network. If the nucleus of an atom changes its characteristics, this may change the entire pattern governing the formation of other elements."

Elements vary

One of the problems with simulations is that no one knows what happens when nuclear reactions move beyond the well-known nuclei and out to the very exotic ones, that are not found in nature.

Atomic nuclei consist of a good mix of protons and neutrons. The definition of an element is determined by the number of protons. The physical characteristics of elements depend also on the number of neutrons. The various states are called isotopes. '

When it gets really hot, such as inside a star or a supernova, neutrons may be released and fuse with other atoms. When one of the neutrons of an atom emits an electron, the neutron turns into a proton. Then the atom has been transformed into a heavier element.

Nuclear physicists can calculate the probability of a physical transition between different elements. The known isotopes have been measured in laboratories. However, there are many isotopes which have not been measured. The limits are unknown.

"We do not know what happens when nuclear reactions in supernova explosions move beyond the table of isotopes. In a matter of seconds, many exotic atoms are formed that do not exist on Earth and which quickly transform into stable elements. Since we have no data on these exotic nuclei, the astrophysicists have to make many assumptions about their properties."

In a supernova explosion you need a large enough number of neutrons available. At the moment there seems to be more protons than neutrons in a supernova.

"In order to get the necessary reactions in a supernova, we must have neutron-rich nuclei."

This is precisely where Larsen's research comes in. As long as the supernova has a sufficient amount of neutrons, astrophysicists can, with the help of the new findings from the University of Oslo, produce better simulations of the formation of elements in supernovae.


Story Source:

The above story is based on materials provided by University of Oslo. The original article was written by Yngve Vogt. Note: Materials may be edited for content and length.


Cite This Page:

University of Oslo. "New insight into atomic nuclei may explain how supernovas formed elements crucial to humankind." ScienceDaily. ScienceDaily, 8 May 2012. <www.sciencedaily.com/releases/2012/05/120508094346.htm>.
University of Oslo. (2012, May 8). New insight into atomic nuclei may explain how supernovas formed elements crucial to humankind. ScienceDaily. Retrieved October 1, 2014 from www.sciencedaily.com/releases/2012/05/120508094346.htm
University of Oslo. "New insight into atomic nuclei may explain how supernovas formed elements crucial to humankind." ScienceDaily. www.sciencedaily.com/releases/2012/05/120508094346.htm (accessed October 1, 2014).

Share This



More Space & Time News

Wednesday, October 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

French Apple Fans Discover the Apple Watch

French Apple Fans Discover the Apple Watch

AFP (Sep. 30, 2014) — Apple fans in France discover the latest toy, the Apple Watch. The watch comes in two sizes and an array of interchangeable, fashionable wrist straps. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
The Water You Drink Might Be Older Than The Sun

The Water You Drink Might Be Older Than The Sun

Newsy (Sep. 27, 2014) — Researchers at the University of Michigan simulated the birth of planets and our sun to determine whether water in the solar system predates the sun. Video provided by Newsy
Powered by NewsLook.com
First Woman Cosmonaut in 17 Years Blasts Off for ISS

First Woman Cosmonaut in 17 Years Blasts Off for ISS

AFP (Sep. 26, 2014) — A Russian Soyuz spacecraft carrying an American astronaut and two Russian cosmonauts, including the first woman cosmonaut in 17 years, blasted off on schedule Friday. Duration: 00:35 Video provided by AFP
Powered by NewsLook.com
Water Discovery On Small Planet Could Be Key To Earth 2.0

Water Discovery On Small Planet Could Be Key To Earth 2.0

Newsy (Sep. 25, 2014) — Scientists have discovered traces of water in the atmosphere of a distant, Neptune-sized planet. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins