A Cork Institute of Technology group is leading Irish efforts to learn moreabout quasars, the brightest objects in the universe, reports Dick Ahlstrom
Think of the brightest sunlight on the clearest day of the year. Now multiply it a millionfold. Such an intense light would still be hopelessly dim compared with the colossal output from a quasar.
Nothing compares to a quasar when it comes to giving off a continuous source of light, explains Dr Niall Smith, a lecturer in the department of applied physics and instrumentation at Cork Institute of Technology.
Our Milky Way galaxy contains about 100,000 million stars; a single quasar can send out up to 10 million times their combined light, lasting a million years. The celebrated gamma-ray bursts can give off more light again but last for mere seconds, so quasars still top the list for continuous light output, says Smith.
He leads five researchers who form part of an EU network of laboratories working towards a better understanding of these enigmatic objects.
The institute also has a lead role in Irish involvement in the network, with collaborating researchers at University College Dublin, University College Cork and Tallaght Institute of Technology.
Current theories assume that a super-massive black hole lurks at the heart of a quasar. Material drawn into its unbreakable hold is immediately converted to energy as radiation in wavelengths from radio up to gamma frequencies. Beyond that they are a mystery.
"They have a life cycle we don't fully understand," says Smith. "We don't know what is happening in the centre as material flows in and radiation is given off."
Quasars also have a tendency to flare, pulsing out short bursts of extra energy for unexplained reasons. About 10 per cent of all quasars also emit strong jets of radiation.
"These are powerful jets. If you were in the line of a jet you would be in trouble."
The European network involves labs looking at the objects at various wavelengths. The Cork group specialises in optical wavelengths; it has some of the best visible-light data on quasars available anywhere thanks to a new camera designed by a Belfast company, Andor. (The Andor camera was described in a Science Today report on October 30th.)
The team used it at the 2.2-metre telescope at Calar Alto, Spain. Existing devices can take one frame a minute; the new camera can take several frames a second, an important consideration for the data being sought.
Short flares cause the light output of a quasar to jump temporarily. "What we are looking for is variation in the light output of the quasar, both very small variations and very rapid variations. That is why the Andor camera was so important for us."
The higher resolution allowed the Cork researchers to capture these very rapid variations in light intensity, which can be plotted along "light curves", explains Smith.
"It allowed us to generate light curves that are very accurate. We found some very nice light curves where we could follow the flare over time. We were looking at a quasar that has a very powerful jet shining towards us. This type of object allows us to learn more about the physics of what is going on in the jet."
This week the network has been ganging up on a quasar known as 0716+741, the same object studied with the new camera during two runs in January and September at Calar Alto, says Smith. "There is an intensive campaign going on with this one object." It includes 11 radio telescopes, 10 optical telescopes and satellites, all looking at the quasar at different frequencies.
"These jets are millions of light years long," explains Smith, and short-term flares can arise along small sections of the jet. "If you see a flare, you can get an idea of the size and get some idea of what is going on."