A GALACTIC PUZZLE SOLVED? THREADS TIE IT TOGETHER

A tangle of spidery filaments stretches outward from the giant elliptical galaxy NGC 1275 as if they were dendrites of an intergalactic nerve cell.

A tangle of spidery filaments stretches outward from the giant elliptical galaxy NGC 1275 as if they were dendrites of an intergalactic nerve cell. NGC 1275, 235 million light-years from Earth near the centre of a clump of galaxies known as the Perseus cluster, has posed a puzzle: How have these filaments, which are made of gas much cooler than the surrounding intergalactic cloud, persisted for perhaps 100 million years? Why haven’t they warmed, dissipated or collapsed to form stars? Images taken by the Hubble Space Telescope, with 10 times the resolution of earlier photographs, reveal that the filaments, about 1,500

light-years wide and hundreds of thousands of light-years long, are themselves made of finer threads—smaller structures about 200 light-years wide and 20,000 light-years long. The cold gas is pushed out by waves of radiation emanating from the giant black hole at the centre of the galaxy. Small is relative, of course. Each thread contains as much mass as 1 million Suns.
With the new information, a team led by Andrew C. Fabian, an astrophysicist at the University of Cambridge, calculated that weak magnetic fields, about one ten-thousandth as strong as the Earth’s field, exert enough force on the charged particles in the threads to keep them together, perhaps answering the puzzle.

IN SALMONELLA ATTACK, TAKING ONE FOR THE TEAM
To make you sick, some salmonella bacteria make the ultimate sacrifice. A tainted piece of lettuce or egg might carry thousands of salmonella bacteria. But even that many salmonella cannot muscle out the helpful bacteria that live day in and day out in the intestines. So, about 15 per cent of the salmonella go on a suicide mission, invading the intestinal walls. There, the immune system handily wipes them out. But that also sets off a wider immune response that, while attacking the salmonella within the gut, also wipes out many other micro-organisms.
“This inflammation removes many of the competitors, so the second group which waited outside can proliferate,” said Martin Ackermann, a professor of environmental sciences at the Swiss Federal Institute of Technology in Zurich. The research, which combined bacterial biology with the mathematical models of game theory, illustrates how even simple organisms appear to cooperate for the greater good of their species.
The suicidal salmonella are genetically identical to their more reserved kin; a random process within individual bacteria appears to cause some of them to sign up for the suicide mission. The researchers showed that this self-sacrifice works if it benefits members of the species alone. If a mutation created a salmonella strain that always opted out of the suicide attacks, these salmonella would benefit in the short term within the gut, but they would have trouble spreading to the next victim.
NYT