Helium might be responsible for setting solar winds minimum speed

Scientists seem to finally have the answer why the speed of solar winds, the constant stream of electrically charged particles emanating from the Sun, never drops to below 260 kilometres per second.

London, May 19 : Scientists seem to finally have the answer why the speed of solar winds, the constant stream of electrically charged particles emanating from the Sun, never drops to below 260 kilometres per second.

NASA astronomers have said helium in the Sun might be responsible for setting this minimum speed.

In their study, Justin Kasper and his colleagues at MIT in Cambridge, US found a connection between wind speed and the amount of helium it contained; the faster the wind, the more helium was present in solar winds, the researchers found.

At higher wind speeds of around 500 kilometres per second, the proportion of helium was about four percent, but at the lower limit of 260 kilometres per second, the proportion dropped to almost zero percent.

Helium, because of its two protons and two neutrons, is about four times as massive as hydrogen, and is not easily accelerated by the processes that fling hydrogen nuclei from the Sun.

So, it is possible that helium is getting dragged along by the hydrogen, which by moving at below 260 kilometres per second simply cannot overcome the drag, thereby setting about the minimum speed.

"It seems to imply that the hydrogen has to get up to a sufficient speed or it's not able to get past the helium. These observations really say we need to do a lot more work on the role helium plays in regulating the solar wind," said Kasper.

According to Kasper, helium might also play a role in solar outbursts, called coronal mass ejections (CME), which are known to contain about 20 percent helium, a much higher proportion than in the normal solar wind.

Since helium particles are heavier than hydrogen particles, a 20 percent helium abundance means half the mass of the material is helium. Understanding how the helium affects the behaviour of the material that makes up CMEs could therefore be important for understanding how these eruptions unfold, New Scientist quoted Kasper as saying.

He said the new findings could help scientists better understand solar outbursts that can interfere with GPS signals and pose a danger to astronauts.

However, solar physicist David Hathaway of NASA's Goddard Space Flight Center in Greenbelt, Maryland, has opined that other phenomena, and "not helium", might explain the observations.

The findings appear in The Astrophysical Journal.

ANI