Tag: Neutron Star Mergers

New Astrophysics Study proposes another process by which the heaviest elements, such as Gold can be created by Black Holes.

Back in High School we all learned that the objects in our daily life here on Earth are made up of a large number of chemical elements such as oxygen or carbon or iron. We also learned that all of those elements, no matter how different, were themselves made up of only three types of sub-atomic particles the electron, the proton and the neutron. By the way those protons and neutrons are themselves made up of even smaller particles called quarks. At the present time that’s as far down as it goes.

The Periodic Table of the elements, more than 100 different substances, with many different properties, all made from just different combinations of Protons, Neutron and Electrons. (Credit: PubChem)

Now a trillionth of a second after the big bang the Universe was a seething mass of all of the elementary particles that make up what physicists call ‘The Standard Model’. As the Universe expanded and cooled however the quarks combined to form the protons and neutrons. All that took place within the first second after the big bang.

The Standard Model of elementary particles. Physicists think that there is some underlying simplicity beneath this model, like Protons, Neutrons and Electrons for the periodic table, but we haven’t figured it out yet. (Credit: Dreamstime.com)

After that most of the protons just stayed protons becoming hydrogen nuclei so that hydrogen, the simplest element is still the most abundant of all the elements. Later, we think about 2 minutes after the big bang some of the protons and neutrons came together to form helium nuclei. A million years later, as the first stars began to form those were really the only two elements that existed. Before the first stars formed the visible matter in the Universe was about 75% hydrogen and 25% helium by mass. Virtually none of the other elements, like sodium, calcium or copper, were created in the Big Bang.

Our Universe’s baby picture, the Cosmic Microwave Background (CMB). At this point the only chemical elements that existed were Hydrogen and Helium. Where did the rest come from? (Credit: Wikipedia)

So where did all of those elements come from, where did the carbon, oxygen and nitrogen that make up your body come from. Those elements, and many others were made inside of those first stars; they were generated by the fusion reactions that gave energy to those suns. Beginning with fusing hydrogen into helium as a star starts to run out of hydrogen its core becomes hotter and denser so that it begins to fuse helium into carbon and oxygen and then it will fuse carbon and oxygen to make the elements up to iron.

When a star, such as our Sun, reaches the end of its lifetime and is running out of both hydrogen and helium for fuel it starts to expel a large portion of its mass as a planetary nebula like the famous Ring Nebula shown here. This is how the Universe gets most of it’s Oxygen, Nitrogen, Carbon and other light elements up to Iron. (Credit: Sky and Telescope)

Iron is a dead end however because you can’t get any more energy by fusing iron so the star’s core can no longer fight the force of gravity and begins to collapse while the outer regions explode as a massive supernova. In that titanic detonation enough energy is released to produce some of the heavier elements such as silver, tin or iodine. Even so those elements are far less common in the Universe than are elements lighter than iron like carbon and oxygen.

The Crab Nebula is the remenants of a supernova explosion. There’s a lot of the lighter elements here but also a small amount of the heavier elements. (Credit: Wikipedia)

Then there are the heaviest elements of them all, elements like gold or lead or uranium. While a tiny amount of these substances may be created in supernovas astrophysicists now think that much of the heaviest atomic nuclei are produced in an even rarer cosmic event than a supernova, the merger of two neutron stars. This hypothesis is gaining favour thanks to the data obtained by gravity wave detectors like the Ligo experiment that have actually observed neutron star mergers.

With our new Gravity Wave Observatories astronomers can now study the mergers of two neutron stars. Theoretical studies indicate this is another source for even the heaviest elements. (Credit: Forbes)

Now a research group at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt Germany, in cooperation with scientists in Belgium and Japan have conducted computer simulations showing how even the heaviest elements could also be produced in the accretion disks that form around black holes. According to Doctor Oliver Just, an astrophysicist and member of the group, “In our study, we systematically investigated for the first time the conversion rates of neutrons and protons for a large number of disk configurations by means of elaborate computer simulations and we found that the disks are very rich in neutrons as long as certain conditions are met.” Which is a fancy way of saying the heaviest chemical elements could be produced in a black hole’s accretion disk.

First ever image of a Black Hole taken by the Event Horizon Telescope. What you’re actually seeing here is the accretion disk around the Black Hole itself. A new study proposes that the accretion disk of Black Holes may be a source for heavy elements. (Credit: Wikipedia)

As matter is drawn into the black hole from the accretion disk the release of energy is so great that some matter escapes before it enters the black hole. This escaping matter could therefore produce a small but constant output of heavy elements.

As matter is pulled into the Black Hole from its accretion disk so much energy is released that a small amount escapes from the polar regions at relativistic speeds. (Credit: Space.com)

At the moment this is just a hypothetical simulation but certainly the accretion disk of a black hole is a location where there is enough energy being released to produce even the heaviest elements. More data from observations of accretion disks is needed so that the group can refine their simulations and fortunately that data is now becoming available thanks to the work of the Event Horizon Telescope,the astronomers who two years ago released the first actual picture of a black hole. See my post of 17 April 2019.

Signals from radio telescopes around the world were combined to produce a single telescope thousands of kilometers in diameter. This ‘Event Horizon Telescope’ took the first ever image of a Black Hole. (Credit: www.ru.nl)

Where the chemical elements came from is a question that scientists have asked since the idea of atoms and elements was first suggested. Today we know a great deal, but there’s still much more to learn.

Gamma Ray Bursts are the most powerful events ever observed in the entire Universe. Could one ever be a threat to life here on Earth?

Ever since Galileo first pointed his telescope into the night’s sky astronomers have continued to discover ever stranger and more fascinating objects inhabiting this Universe of ours. Surely among the most mysterious are the objects known as Gamma Ray Bursts (GRBs).

What is a GRB? Well, about once a day, somewhere in the Universe an event occurs that releases as much energy in a few seconds as our Sun will generate in its entire life! This energy is observed as a bright burst of gamma rays. For decades little was known about GRBs and it’s only in the last 22 years that astronomers and astrophysicists feel that they have begun to understand something about these strange entities.

Gamma Ray Bursts are thought to be the most energetic events in the entire Universe! (Credit: Futurism)

Even the discovery of GRBs was pretty unusual. It is a fact that GRBs are the first, and so far only astronomical discovery to be made by CIA spy satellites. You see it all started in 1963 when the old Soviet Union agreed to the Nuclear Test Ban Treaty that ended the above ground testing of nuclear weapons. The US didn’t quite trust the Russians however; it was thought that the Soviet’s might try to cheat the ban by testing their weapons in outer space. So the CIA launched a series of satellites known as Vela that were designed to detect the sort of gamma radiation that would accompany any nuclear explosion off the Earth.

With the signing of the Nuclear Test Ban Treaty in 1963 the World’s Atomic powers agreed to halt above ground tests of nuclear weapons. (Credit: YouTube)

On July 2 in 1967 the Vela 2 and Vela 3 satellites detected a quick burst of gamma rays but it was soon realized that the burst wasn’t caused by the Russians. Using the data from the two satellites scientists at Los Alamos Nation Laboratory found that the radiation had come from somewhere outside of the solar system. Other bursts were soon detected as well but since the entire Vela program was classified as Top Secret astronomers didn’t get to hear about the discovery until 1973.

The VELA gamma ray detecting satellites were launched into space to monitor the Soviet Union’s Compliance with the Nuclear Test Ban Treaty. Instead they discovered the existence of Gamma Ray Bursts. (Credit: Flickr)

Even after the world’s astronomers knew about the existence of gamma ray bursts progress in understanding them was very slow. Think about it, since gamma rays are blocked by Earth’s atmosphere GRBs can only be detected by specialized satellites. Add to that the fact that GRBs rarely last more than a minute and that they can appear in any part in the sky and you can understand how hard it was to obtain any real data about them. 

The Earth’s Atmosphere blocks most forms of electromagnetic radiation allowing only visible light and radio waves to reach the surface. (Credit: Pinterest)

What astronomers wanted to learn most of all was whether or not GRBs had any other electromagnetic component to them. That is, did an optical, radio or perhaps X-ray flash accompany the gamma ray emissions. In order to do this astronomers had to develop a fast reaction network that would quickly communicate the news that a GRB had been detected to astronomers around the world so that other instruments could be brought in action.

Success finally came in February 1997 when the satellite BeppoSax detected GRB 970228 (GRBs are named by the date of their detection YY/MM/DD). Within hours both an X-ray and an optical glow were detected from the same source, a very dim, distant galaxy. Further such detections soon confirmed that GRBs came from such extremely distant galaxies, most of them many billions of light years away. So distant are the locations of GRBs that in order to appear so bright in our sky they must be the most powerful explosions in the entire Universe.

The BeppoSAX Satellite was designed and launched specifically to study GRBs. (Credit: SlidePlayer)

So what are these GRBs? What makes them so energetic? To be honest there’s still a lot to be learned but a consensus of opinion is growing that there are actually two distinct types of GRBs.

Those that last for a somewhat longer length of time, longer than 30 seconds, are the initial stages of a core collapse supernova. That is the death of a star so massive that it never really settled down like a normal star but instead just implodes after a few million years into a black hole. All of the well-studied GRBs fit this model remarkably well, including their location within galaxies that are undergoing rapid star formation, places where such massive, short-lived stars are far more common.

One interesting feature of this model is that as the star collapses it rotates much more rapidly, just as an ice skater will do when they pull in their arms during a spin. This increase in rotation speed generates a enormous magnetic field at the star’s poles causing the gamma rays that are emitted to squirt out from the poles like the beams of light from a lighthouse. This concentrates the power of the gamma rays into two narrow beams making the GRB look much brighter in the directions those beams travel.

The energy of long duration GRBs is concentrated into two narrow beams light the light from a lighthouse. (Credit: AAS Nova)

If this lighthouse feature of GRBs is true that implies that we are only seeing a small fraction of all GRBs, only those that are pointing at us. It also means that GRBs are not quite as powerful since their energy is focused into the beams. Again, this model fits the data collected for longer duration GRBs that make up about 70% of those that have been observed.

There are also short term GRBs, whose duration averages less than half a second and which make up about 30% of the total observed. Because they are fewer in number and shorter in duration these GRBs are harder to study and therefore less well understood. Several models have been suggested for them but the recent simultaneous observation of a GRB (GRB170817A) only 1.7 seconds after a gravity wave was detected by the LIGO gravity wave observatories implies a direct connection. Based on the nature of the gravity wave observed the event was a merger of two neutron stars. Therefore at least some short period GRBs are the result of neutron stars colliding to form a black hole or a black hole devouring a neutron star.

A Merger of Neutron Stars releases both a GRB and power Gravity waves. (Credit: AAS Nova)

So, if these GRBs are the most powerful explosions in the entire Universe, could they be any danger to us? Are their any stars in our galactic neighborhood that could collapse and generate a GRB? And what damage would a nearby GRB do?

In fact there are a couple of possible candidates known to astronomers. The stars Eta Carinae and WR 104 are both hugely massive stars that could collapse into black holes sometime in the next million or so years. Of the two WR 104 is closest at a distance of only 8,000 light years.

Eta Carena (l.) and WR104 (r.) are the most most massive and powerful stars known. Either couls someday collapse into a black hole triggering a GRB. (Credit: Gresham College)

If WR 104 were to generate a GRB, and if that GRB were aimed at Earth our atmosphere would protect us from the initial burst of gamma and X-rays, only a spike in the Ultra-violet lasting a few minutes would be seen. The long-term effects are much less pleasant however because the gamma and X-rays striking the atmosphere would cause oxygen and nitrogen to combine to form nitrogen oxide and nitrogen dioxide gasses. Both of these gasses are known destroyers of ozone, the form of oxygen in the upper atmosphere that protects us from the Sun’s UV rays. Also the gasses could combine with water vapour in the air to form droplets of nitric acid that would rain down causing further damage.

The Earth’s Ozone layer protects us from the cancer causing UV light from the Sun. Credit: UCAR)

Of course all of that is just speculation, we really have no idea what would happen here if a GRB from a star as close as WR 104 should strike the Earth. Before you start to panic however remember that GRBs are very rare, only one per day in the entire Universe. Let’s be honest, we’re a far greater danger to ourselves than Gamma Ray Bursts are!