NASA launch today aims to measure what lies between

Part one of a two-stage experiment to learn about the Intergalactic Medium is set for go. Andrew Masterson reports.

NASA staff monitor the launch of a sounding rocket.
NASA staff monitor the launch of a sounding rocket.

A NASA sub-orbital rocket launch and 15-minute test flight scheduled for today could help cosmologists better understand the nature and origin of the of the hot diffuse gas that fills the monumental empty spaces of the universe.

Weather permitting, the agency will send up a Black Brandt IX rocket containing a hyper-sensitive piece of equipment set to measure the ultraviolet radiation streaming from a hot young star called Beta Canis Major.

The Black Brandt IX is part of a range developed by NASA and known as sounding rockets. The vehicles are geared to short duration, low altitude flights and are used to both field test equipment and to conduct experiments in astrophysics.

Today’s launch marks the first of a two-stage investigation known as the Dual-channel Extreme Ultraviolet Continuum Experiment (DEUCE).

The research aims to better understand the matter that exists in the vast spaces between galaxies, known as the Intergalactic Medium, or IGM.

The IGM is poorly understood at present. Temperatures within it are thought to hit millions of degrees Kelvin, yet it has a density of less than one atom per cubic metre. Originally thought to comprise only hydrogen and helium remnants of the Big Bang, later research found that it also contains metallic elements – thought to be “pollution” dispersed by galactic winds.

Atoms within the IGM are ionised – that is, the electrons have been split away from the nuclei. This is thought by some scientists to be caused by high-energy ultraviolet radiation produced by star-forming galaxies. It has proved difficult to test the theory from Earth, however, because out planet’s atmosphere blocks a large amount of the ultraviolet light streaming towards it.

Using a sounding rocket, thus, allows researchers to get equipment high enough above the ground to escape the distorting effects of the atmosphere and take more accurate readings.

The experiment uses a microchannel plate detector – the largest ever launched into space – to measure the starlight from Beta Canis Major. The work will double as a test for the detector itself – variations of which are likely to be key components on future large scale missions.

The star was chosen as a target because it is close enough to Earth that the ultraviolet light it emits is not completely absorbed by interstellar gas, making a usable reading possible. A second target star in the same constellation, Epsilon Canis Major, will be the target of the second DEUCE experiment, in December.

"It's a hard measurement to make, because there still is neutral hydrogen between stars that is extremely effective at absorbing the starlight at these wavelengths," says Nicholas Erickson from the University of Colorado, who is working on the project.

"To be seen at Earth, you need a really bright star that's close by, and there are only two stars that are viable candidates for this measurement."

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