‘Star Comb’ joins quest for Earthlike planets


Share post:

If there is life on other planets, a laser frequency comb developed at the National Institute of Standards and Technology (NIST) may help find it. 

NIST researchers and collaborators measured the frequencies, or colors, of infrared starlight (three solid bands with faint tick marks indicating where light is absorbed by the atmosphere) by comparing the missing light to a laser frequency comb reference “ruler” (sets of bright vertical bars indicating precise wavelengths, which increase from left to right). The three sets of starlight and comb light are shown in false color, from deeper orange (the most light) to orange-white (slightly less light) to black (very little light) [Credit: CU/NIST/Penn State]

Such a comb—a tool for precisely measuring frequencies, or colors, of light—has for the first time been used to calibrate measurements of starlight from stars other than the Sun. The good results suggest combs will eventually fulfill their potential to boost the search for Earth-like planets to a new level. 

As described in Optics Express, the comb was transported to the Texas mountains to calibrate a light analyzing instrument called a spectrograph at the Hobby-Eberly telescope. A University of Colorado Boulder (CU) astronomer and Pennsylvania State University students and astronomers collaborated on the project. 

“The comb worked great,” says NIST physicist Scott Diddams. “In a few days, it enabled measurement precision comparable to the very best achieved in the same wavelength range with much more established techniques—and we hope the comb will do much better as the new technique is perfected.” 

The NIST comb calibrated measurements of infrared starlight. This type of light is predominantly emitted by M dwarf stars, which are plentiful in Earth’s part of the galaxy and might have orbiting planets suitable to life. 

To search for planets orbiting distant stars, astronomers look for periodic variations in the apparent colors of starlight over time. A star’s nuclear furnace emits white light, which is modified by elements in the star’s and the Earth’s atmosphere that absorb certain narrow bands of color. Periodic changes in this characteristic “fingerprint” can be caused by the star wobbling from the gravitational pull of an orbiting planet. More than 600 planets have been discovered using star wobble analysis, but a planet analogous to the Earth, with low mass and orbiting at just the right distance from a star—in the so-called “Goldilocks zone”—is hard to detect with conventional technology. 

The wobbling effect is very subtle. Astronomers are limited by the precision of techniques used to measure the starlight, and infrared frequencies in particular can be challenging to measure precisely with conventional tools. But the NIST comb, which spans an infrared wavelength range of 1450—1700 nanometers, provides strong signals at narrowly defined target frequencies and is traceable to international measurement standards. Used with a spectrograph, the frequency comb can act like a very precise ruler to calibrate and track the exact colors in the star’s fingerprint and detect any periodic variations. 

The NIST comb measured radial velocity—star wobble—with a precision of about 10 meters per second, comparable to the best ever achieved in the infrared region of the electromagnetic spectrum. The first field results are limited by the short observation time and technical issues associated with the newly developed experimental approach. The team hopes to soon improve precision to 1 meter per second, roughly the limit to date for measuring visible light from the Sun—which would put the technique at the cutting edge of infrared astronomy. The NIST comb has the inherent capability to measure star wobble of just a few centimeters per second, 100 times better, although limitations in the spectrograph and in the stability of the star itself may constrain the ultimate precision. 

CU graduate student Gabe Ycas, along with Diddams and CU astronomer Steve Osterman, created the frequency comb, which has widely spaced “teeth,” or calibration points, tailored to the reading capability of spectrographs. This work was supported by NIST and the National Science Foundation. Penn State is a partner in the telescope and spectrograph. 

Author: Laura Ost | Source: National Institute of Standards and Technology [March 07, 2012]



Related articles

Out of the blue: Medieval fragments yield surprises

Analyzing pigments in medieval illuminated manuscript pages at the Cornell High Energy Synchrotron Source (CHESS) is opening up...

Excavations at Sicyon reveal residential quarters

A series of fundamental questions concerning the organisation of ancient Sicyon and its relationship with its neighbours are...

A seismograph for ancient earthquakes

Earthquakes are one of the world's biggest enigmas — impossible to predict and able to wreak untold...

UNESCO starts excavations at two Nepal monuments

Continuing a mission initiated last year to restore Nepal’s cultural heritage damaged in the 2015 earthquake, UNESCO has...

Shot away from its companion, giant star makes waves

Like a ship plowing through still waters, the giant star Zeta Ophiuchi is speeding through space, making waves...

Fossil bone growth reveals the ancestry of mammalian ‘warm-bloodedness’

One associated effect of being 'warm-blooded' is a relatively fast growth-rate. Mammals (and birds, who are also 'warm-blooded')...

Genome of the Black Death reveals evidence for an antique bubonic plague pandemic

In a comparison of more than 300 contemporary strains of Yersinia pestis, the bacterium that causes bubonic plague,...

Bronze Age Iberia received fewer Steppe invaders than the rest of Europe

The genomes of individuals who lived on the Iberian Peninsula in the Bronze Age had minor genetic input...