artist's rendering of what the ancient Milky Way may have looked like

Photons in space: the struggle is real

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Jan 19, 2017

Photons are the reason that our Earthling eyes (via immensely powerful telescopes) can see galaxies so many light-years away. These light-transmitting particles are also the reason scientists could soon be illuminating an epic struggle between darkness and light in the ancient Milky Way.

While this may sound like something out of a fantasy novel, researchers investigating the origins of some of the youngest alien galaxies currently visible from Earth have observed that these galaxies act as light dungeons that refuse to let go of their photons. Ethereal haloes of photons that have been through some intense struggles surround these galaxies; this otherworldly glow is only visible because a minority of photons were able to escape.

Light is made of photons. They are simultaneously particles, which is why they can transfer energy by colliding with atoms and waves, which explains why light can refract. Astronomers involved in this study were searching for Lyman-alpha emissions, which occur when the electrons in hydrogen atoms sink to the lowest energy level within those atoms. The resulting photons that emerge have a distinct amount of energy that makes them relatively easy to find.

However, the fact that so few had managed to escape their galaxy's grip and are visible as that ghostly light was telling. The journey these photons went through must have been treacherous.

The green haze in the photo is a halo of dust and debris from which Lyman-alpha photons are struggling to escape.

"Newly born stars in very distant galaxies are hot enough to break apart hydrogen in surrounding clouds of gas, which then shines brightly in Lyman-alpha light, in theory the strongest such features observable in a distant galaxy," explained astronomer Jorryt Matthee of the University of Leiden. "Yet in practice, Lyman-alpha photons struggle to escape galaxies as gas and dust block and diverge their travel paths, making it a complex process to understand."

Uninhibited photons zoom indefinitely through space in a straight line. These photons were born into a dusty and gaseous fog, a labyrinth of particles that kept crashing into them and sending them off course into some other dark shadow of their galaxy. Astronomers at the University of Lancaster and the University of Leiden used the Wide Field Camera of the Isaac Newton Telescope to survey 1,000 far-away galaxies for Lyman-alpha emissions. What collisions these photons had, and with which atoms and molecules, reveal critical details about a galaxy's chemical composition that can bring its activity over millions and billions of years to light. 

By holding up their findings against predictions of Lyman-alpha photon behavior specific to these galaxies, they determined that a mere 10% of these photons escaped. The rest were doomed to being endlessly absorbed and re-absorbed by the menacing fog — hence those phantom haloes.

Scientists involved in the study now believe that photons also had to navigate such a murky ocean of microscopic debris in the early Milky Way. Why this happens is still unknown. The next phase of research will involve using even more advanced technology to study haloes in more distant galaxies. Until then, they remain shrouded in dust and mystery.

(via Astronomy.com)