Imagine the weight of a sugar cube balanced on the end of a spoon, then compare this with a cube of lead or gold, or any other dense material. The heaviest thing you could image would be as nothing compared to the weight of the material that makes up a Black Hole.
A single sugar cube-sized lump would weight in at a tremendous and incomprehensible 5,000 million tonnes. Its density is so spectacular that should you drop the cube off the spoon it would probably crush down through the Earth's surface, stopping only after it arrived at the core.
No scales on Earth would be able to handle such material, but scientists are still able to estimate the mass of Black Holes, those gravitational monsters with an attractive force so powerful that not even light can escape their mighty pull.
Dr Paul Callanan, a lecturer in physics and astronomy at University College Cork is involved in international studies to "weigh" Black Holes. He started this work as a post-doctoral researcher at Oxford and then Harvard and he continues it in collaboration with a colleague at the University of California, Berkeley, Prof Alex Filippenko.
"They do all sorts of very strange things," Dr Callanan said, while describing these remarkable objects. "There is no way we could study that material here on Earth."
Scientists want to answer basic questions about them, he said, such as where are they; how many of them are there; are there any close to Earth; and what size is the behemoth Black Hole that lurks at the heart of our galaxy. They also want to differentiate between Black Holes and other very massive objects such as Neutron stars and White Dwarf stars.
The gravitational pull of such dense objects often traps a stellar companion, a passing star that becomes locked into orbit. Some stars remain in this orbital two-step but others are slowly cannibalised by the Black Hole, which will suck away matter to form an "accretion disc" around itself, Dr Callanan explained.
Black Holes are so named because they give off no light and can't be easily observed. Their gravitational pull - and hence their mass - can be estimated, however, because of their influence on any companion star, Dr Callanan said. These stars get squished out of their normal spherical shape because of gravity's grip.
Centrifugal force acting on the star will keep it in orbit but it will distort into a "teardrop" shape, Dr Callanan said. "The degree to which the star is bent out of shape is a measure of the mass of the Black Hole."
More clues can be derived from the star's orbital speed. "The more massive the Black Hole is, the faster the star has to orbit. Once we have the mass, we have the data we need to decide whether the object is a Black Hole, a Neutron Star or White Dwarf."
A Neutron Star packs the mass of our sun into a sphere just 20 km across. The sun's diameter is about 700,000 km across. The smaller black holes have between five and 10 solar masses, Dr Callanan said but a central density that is almost infinite.
Dr Callanan makes his observations and analyses data from some of the world's largest telescopes, including the Keck telescopes in Hawaii, which have mirrors 10m across. He and Prof Filippenko have scheduled access to the Kecks this July 21st, 23rd and 25th.
Many of his observations are done at the infrared rather than visible light wavelengths. "Astronomers always want to get the crispest, clearest pictures of the heavens. They hate to see stars twinkling," Dr Callanan said.
Light arriving from the stars is refracted by the atmosphere in the same way that a stick apparently bends when dipped into the water. "The stars don't twinkle so much in the infrared spectrum," he added. "Our Keck images are very sharp compared to optical images."
This same valuable Keck data will in turn be available to students who decide to pursue UCC's new degree course in Astrophysics, which gets underway this autumn. The decision to introduce this degree arose because of significant student interest, he said.
The first two years of the Astrophysics degree programme are general physics, with the last two focusing on astrophysics. The work requires much exposure to computational and computer work, he said, and far from being of limited value to potential employers, the course "is a way of giving students a computational background employers are interested in. Astrophysics is a very computational pursuit."
The UCC astronomy research group has a web site with more information about the new Astrophysics degree programme and is available at: http:// www.astro.ucc.ie