Nasa's Spitzer infrared space telescope ran out of coolant on May15, more than five and a half years after its launch. It has since warmed to a still-frosty 30 degrees Kelvin (about minus 406 degrees Fahrenheit).

Its two shortest wavelength detectors are still functional.

Explaining why the telescope's instruments have to be kept in cool condition and what is the significant difference in the performance between now and before the coolant ran out, Mr. Whitney Clavin, Nasa spokesperson, noted in an email to this correspondent:

"Cold instruments are needed to detect the longest wavelengths of infrared light and Spitzer's instruments detect everything between 3.6 to 160 microns. To detect 160 micron light, without being swamped by the internal thermal glow of the instrument itself, the telescope must be chilled to just a few degrees above absolute zero.

Shorter wavelengths

At shorter wavelengths it can operate at progressively warmer temperatures. At its current ambient temperature of around 30K the two shortest wavelength detectors are fully functional."

This is amply demonstrated by the fact that new images taken with the two detectors show a bustling star forming region, the remains of a star similar to the sun and a swirling galaxy lined with stars.

This shows that Spitzer will continue to deliver worldclass imagery and science during its `warm' mission.

Since its launch in 2003, Spitzer has made many discoveries including planetforming discs around stars, the composition of materials that make up comets, hidden black holes, galaxies billions of light-years away and more.

Warm Spitzer will address many of the same science questions as before including refining estimates of Hubble's constant, or the rate at which our universe is stretching apart.

Hubble's constant

Hubble's constant is the speed at which a distant galactic object is moving away from us divided by the distance of the object from the telescope or the earth.

It can be shown by simple arithmetic that the reciprocal of Hubble's constant is the age of the universe based on the Big Bang theory. Hence it is necessary to refine it to a point of perfection to arrive at an accurate figure for the age of the universe.

On being queried on how the Hubble's constant will be refined by Spitzer, Mr, Clavin said, "an estimate previously was made of the Hubble constant using a relationship between the absolute brightness of a type of variable star (whose brightness varied) called Cepheid and its period of variability.

The method measured the observed brightness and periods of these stars in distant galaxies.

Comparing the observed brightness with the absolute brightness inferred from the period allows one to measure the distance to the object and hence estimate the Hubble constant."

The advantage of doing this in infrared is that the observed brightness will not be affected by the interstellardust between us and the star, and hence the distance measurements will be much more robust.

Keywords: Astronomytelescope

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