Out Of The Darkness

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Simulation of the "Dark Ages," a period between 380,000 years and 4 million years after the Big Bang. The universe was made up primarily of hydrogen in a neutral state, which did not easily connect with any other particles. NASA/WMAP
Simulation of the “Dark Ages” of the universe, a period predicted by theorists to have lasted as long as several hundred million years after the Big Bang.  The first hydrogen atoms in the universe had not yet coalesced into stars and galaxies. (NASA/WMAP)

Before there were planets in our solar system, there was a star that would become our sun.  Before there was a sun, there were older stars and exoplanets throughout the galaxies.

Before there were galaxies with stars and exoplanets, there were galaxies with stars and no planets.  Before there were galaxies without planets, there were massive singular stars.

And before that, there was darkness for more than 100 million years after the Big Bang — a cosmos without much, or at times any, light.

So how did the lights get turned on, setting the stage for all that followed?  Scientists have many theories but so far only limited data.

In the coming years, that is likely to change substantially.

First, the James Webb Space Telescope, scheduled to launch in 2018, will be able to look back at distant galaxies and stars that existed in small or limited numbers during the so called Dark Ages.  They gradually became more prevalent and then suddenly (in astronomical terms) became common.  Called the epoch of cosmic “reionization,” this period is an essential turning point in the evolution of the cosmos.

Less well known but also about to begin pioneering work into how and when the lights came on will be an international consortium led by a team at the University of California, Berkeley. Unlike the space-based JWST,  this effort will use an array of radio telescopes under construction in the South African desert.  The currently small array will expand quickly now thanks in large part to a $9.6 million grant recently announced from the National Science Foundation.

Named the Hydrogen Epoch of Reionization Array (HERA), the project will focus especially on the billion-year process that changed the fundamental particle physics of the universe to allow stars, galaxies and their light burst out like spring flowers after a long winter.  But unlike the JWST, which will be able to observe faint and very early individual galaxies and stars, HERA will be exploring the early universe as a near whole.

 

Before stars and galaxies became common, the universe went through a long period of darkness and semi-darkness, but ended with the Epoch of Reionization. (S.G. Dorgovski & Digital Media Center, Caltech.)
Before stars and galaxies became common, the universe went through a long period of darkness and semi-darkness, but ended with the “Epoch of Reionization.” (S.G. Djorgovski & Digital Media Center, Caltech)

Aaron Parsons, an associate professor at Berkeley and principal investigator of the HERA project, said his team is now ready to grow their proof-of-concept array to a full-fledged observatory with 270 radio telescopes, with science that just might give some solid answers about how the lights came on.

Parsons said they see their effort as a continuation of the earlier pioneering work that identified and mapped the cosmic microwave background radiatio that was produced by another cosmos-changing event some 380,000 years after the Big Bang.

“We have learned a ton about the cosmology of our universe from studies of the cosmic microwave background, but those experiments are observing just the thin shell of light that was emitted from a bunch of protons and electrons that finally combined into neutral hydrogen 380,000 years after the Big Bang,” Parsons said.

“We know from these experiments that the universe started out neutral {at that point}, and we know that it ended ionized, and we are trying to map out how it transitioned between those two.”

Aaron Parsons, associate professor of astronomy at the University of California, Berkeley, and the principal investigator of the HERA prject.
Aaron Parsons, associate professor of astronomy at the University of California, Berkeley, and the principal investigator of the HERA prject.

More specifically, here is what cosmologists and astrophysicists theorize or know happened:

The Big Bang produced a scorching cauldron of  particles that had electrical charge.  That condition ended with the ‘recombination” event that joined protons and neutrons together to form atomic hydrogen, and as a result produced the cosmic microwave background radiation.

What followed was 100 million or more years of abject darkness because the atomic hydrogen was neutral and unable to do much of anything.  Some relatively few stars appeared in those Dark Ages, when enough gas clumped together and set off a star-forming gravitational collapse.

Those stars, and later dwarf galaxies, emitted photons which had the effect of splitting (or ionizing) the hydrogen that surrounded them — creating bubbles of charged hydrogen (and some helium) in a vast ocean of neutral hydrogen.

Much remains unknown about how and when the population of stars and galaxies grew over the ensuing hundreds of millions of years during this epoch of reionization.  But a time came, an estimated one billion years after the Big Bang, when the islands of split hydrogen turned into a universe of split hydrogen. That made widescale star and galaxy formation possible.

Many astronomers study primordial stars and galaxies to learn about this still mysterious process, but the HERA project will analyze instead how those earliest celestial objects changed the nature of intergalactic space.  And that essentially means capturing tiny changes in the vast universe of uncharged hydrogen during and after the Dark Ages, since hydrogen was most of what was present.

As Parsons explained it, the changes within hydrogen atoms they are looking for were weak and occurred only infrequently — perhaps once in 10 million years for a single atom of hydrogen.  “But there’s an awful lot of hydrogen out there, and that allows the weakness to be an advantage.  That means we can see through clouds, can see deep into the hydrogen clouds,” and that allows for observing on a much longer time scale.

The goal of the HERA project is, most broadly, to trace those minute changes in hydrogen from about 100 million years after the Big Bang to one billion years after, when the epoch of reionization culminated with a conclusive turning on of the universe.

An artist rendering of the "bubbles" of ionized atoms theorized to have surrounded the earliest stars. As Parsons explained: "The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today." Illustration from Scientific AmericanAn artist rendering of the "bubbles" of ionized atoms that surrounded the earliest stars. As Parsons explained: "The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today." Illustration from Scientific American
An artist rendering of the “bubbles” of ionized atoms theorized to have surrounded the earliest stars. As Parsons explained: “The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today.” (Illustration from Scientific American)

The HERA array currently has 19 radio telescopes, will grow to 37 soon, and to 270 in 2018.  The team hopes to some day expand to 350 telescopes.  Each is a of radio dish looking fixedly upwards and measuring primordial radiation.  It was originally emitted at a wavelength of 21 centimeters, a  key spectral tracer for the neutral hydrogen atom.  The photons have been been stretched by a factor of 10 or more since it was emitted some 13 billion years ago, making the detections more easily measured.

The signal is nonetheless weak and has been difficult to measure. Previous experiments, such as the UC Berkeley-led Precision Array Probing the Epoch of Reionization (PAPER) in South Africa and the Murchison Widefield Array (MWA) in Australia, have not been sufficiently powerful and sensitive.  But HERA is much more powerful and hopes are high.

The researchers will be looking for the boundaries between those bubbles of ionized hydrogen around early stars — which are invisible to HERA — and the surrounding neutral or atomic hydrogen being measured.  By tuning the receiver to different wavelengths, they can map the bubble boundaries at different distances to follow the the evolution of the bubbles over time.

HERA is being constructed at the Karoo desert site where PAPER was deployed.  Joining the Berkeley team will be scientists from England, South Africa, Italy, MIT, the National Radio Astronomical Observatory, the University of Washington, Arizona State University and others.

HERA was recently granted the status of a precursor telescope for the Square Kilometer Array (SKA), an ambitious project to build a vast collection of radio dishes around Africa and Australia — thereby creating the largest astronomical observatory of all time.  HERA is located close by one of the South African SKA sites.

The HERA present:

 

The HERA telescope as built so far. (The HERA team)
The HERA telescope as built so far. (The HERA team)

The HERA future:

An artist rendering of the HERA telescope when it has grown to 220 dishes, scheduled to occur in 2018. (The HERA team)
An artist rendering of the HERA telescope when it has grown to 220 dishes, scheduled to occur in 2018. (The HERA team)

“Many Worlds” generally focuses on exoplanet science, so perhaps you’re wondering why you’re reading about the early universe, reionization and a radio telescope that will attempt to unravel its mysteries.  One reason is simply that the subject is most intriguing, but also it speaks to two important aspects of exoplanet science.

The first is cosmic evolution, the many phenomena and processes that have led to a universe that features billions of planets and at least one (and most likely more) that hosts life.

The Dark Ages and epoch of reionization set the stage for a far more active universe, including supernova that explode and in the process produce otherwise absent carbon, oxygen, phosophrus and many of the elements needed for planets and for life are formed.  Clearly, knowing more about how the stars, galaxies and interstellar medium evolved allows for deeper understandings of the history and characteristics of exoplanets.

But there is a technical connection between HERA and exoplanets as well.  The array may well be quite useful in detecting certain important types of exoplanets — those with magnetic fields.

Parsons explained that when a host star emits a strong coronal mass ejection,  the flare often comes into contact with orbiting exoplanets.  Scientists know from studying Jupiter, which has an ionosphere and thus a magnetic field, that when the CME hits that field a radio pulse or burst is registered.

“In principle this could happen with lots of planets,” Parsons said.  “A host star is active, sends out a big flare, it interacts with the magnetic field around a planet, and we could measure it.

“Potentially, we could detect planets this way, but more unique is that we can identify planets with magnetic fields.  It’s not clear what role magnetic fields have in making life possible, but the Earth does have a strong magnetic field that protects us.  That’s probably not an accident, and so it would be very valuable to identify planets with magnetic fields.”

So it’s possible that the effort to understand the epoch of reionization just might help uncover a trove of habitable planets.

 

 

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Faint Worlds On the Far Horizon

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Faintest distant galaxy ever detected, formed only 400 million years after the Big Bang. NASA, ESA, and L. Infante (Pontificia Universidad Catolica de Chile)
Faintest distant galaxy ever detected, formed only 400 million years after the Big Bang. NASA, ESA, and L. Infante (Pontificia Universidad Catolica de Chile)

For thinking about the enormity of the canvas of potential suns and exoplanets, I find images like this and what they tell us to be an awkward combination of fascinating and daunting.

This is an image that, using the combined capabilities of NASA’s Hubble and Spitzer space telescopes, shows what is being described as the faintest object, and one of very oldest, ever seen in the early universe.  It is a small, low mass, low luminosity and low size protogalaxy as it existed some 13.4 billion years ago, about 4oo million years after the big bang.

The team has nicknamed the object Tayna, which means “first-born” in Aymara, a language spoken in the Andes and Altiplano regions of South America.

Though Hubble and Spitzer have detected other galaxies that appear to be slightly further away, and thus older, Tayna represents a smaller, fainter class of newly forming galaxies that until now have largely evaded detection. These very dim bodies may offer new insight into the formation and evolution of the first galaxies — the “lighting of the universe” that occurred after several hundred million years of darkness following the big bang and its subsequent explosion of energy.

This is an illustration by Adolf Schaller from the Hubble Gallery (NASA). It is public domain. It shows colliding protogalaxies less than 1 billion years afer the big bang.
This is an illustration by Adolf Schaller from the Hubble Gallery and shows
colliding protogalaxies less than 1 billion years after the big bang. (NASA)

Detecting and trying to understand these earliest galaxies is somewhat like the drive of paleo-anthropologists to find older and older fossil examples of early man. Each older specimen provides insight into the evolutionary process that created us, just as each discovery of an older, or less developed, early galaxy helps tease out some of the hows and whys of the formation of the universe.

Leopoldo Infante, an astronomer at Pontifical Catholic University of Chile, is the lead author of last week’s Astrophysical Journal article on the faintest early galaxy.  He said there is good reason to conclude there were many more of these earliest protogalaxies than the larger ones at the time, and that they were key in the “reionization” of the universe — the process through which the universe’s early “dark ages” were gradually ended by the formation of more and more luminous stars and galaxies..

But the process of detecting these very early protogalaxies is only beginning, he said, and will pick up real speed only when the NASA’s James Webb Space Telescope (scheduled to be launched in 2018) is up and operating.  The Webb will be able to see considerably further back in time than the Hubble or Spitzer.

Estimates of how many galaxies might exist in the universe are in flux, with recent studies producing results ranging from 100 to 225 billion.  On average a galaxy will have some 100 billion stars, giving the universe a low-end estimate of 10,000,000,000,000,000,000,000 stars.

When it comes to planets, a consensus of sorts has formed around the conclusion that in the Milky Way, and perhaps elsewhere, there is on average at least one planet per star.  So assuming that the planetary dynamics of our galaxy are similar to those of others, that’s an awful lot of potential exoplanets.

PSR B1620-26 b is an extrasolar planet located approximately 12,400 light-years away from Earth in the constellation of Scorpius. It bears the unofficial nicknames "Methuselah" and "the Genesis planet" due to its extreme age
PSR B1620-26 b is an extrasolar planet located approximately 12,400 light-years away from Earth in the constellation of Scorpius. It bears the unofficial nicknames “Methuselah” and “the Genesis planet” due to its extreme age. (NASA and G. Bacon, STScI)

All this has significant implications for the field of exoplanet research.

“We know that basically, planets form at about the same time as their stars from all the leftover dust and gas kicked up,” said Joel Green, Project Scientist at Space Telescope Science Institute’s Office of Public Outreach (STScI.)  The Institute operates the science for the Hubble Space Telescope as an international observatory.

“The earliest planets may have been very different kinds of planets because there was not as much metallicity (heavier elements) in those stars.  But as soon as you have stars, you have planets.”

He said that in theory, that means that when the very earliest stars formed — during a time when the universe was essentially dark — planets were formed too. “They don’t need a universe of light to form; they need one star.”

The most ancient exoplanet detected so far (PSR B1620-26 b) has had a rather unusual history, first born 12.7 billion years ago outside of a “globular cluster”  of stars (a comparatively older, compact group of up to a million old stars, held together by mutual gravitation), it then migrated closer to the cluster and into a rough astrophysical neighborhood. As viewed today, it orbits a pair of burned-out stars in the crowded core of a globular star cluster. It was first identified as a possible planet in 1992 — before the detection of 51 Pegasi b — but it took more than a decade to confirm that it is.

The oldest known exoplanet solar system is Kepler -444, formed 11.2 billion years ago in the Milky Way, itself 13.2 billion years old. Located in the constellation Lyra  116 light-years away, it hosts five rocky planets, all orbiting close to their sun.

Kepler-444 hosts five Earth-sized planets in very compact orbits. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist's conception. Credit: Tiago Campante/Peter DevineKepler-444 is a metal-poor Sun-like star located in the constellation Lyra, 116.4 light-years away. Also known as HIP 94931, KIC 6278762, KOI-3158, and LHS 3450, this pale yellow-orange star is very bright and can be easily seen with binoculars. It was formed 11.2 billion years ago, when the Universe was less than 20 percent its current age. It is approximately 25 percent smaller than the Sun and substantially cooler.
Kepler-444 hosts five Earth-sized planets in very compact orbits. A metal poor sun (composed largely of hydrogen and helium), it is very bright and easily seen with binoculars. (Tiago Campante/Peter Devine)

The discovery of a solar system with rocky planets of this age (more than twice the age of our solar system’s rocky planet quartet), opens the door to the prospect of an early universe with many more rocky planets than once thought.  That means there could be vast numbers of very ancient Earth-like planets out there.

Returning to the faintest protogalaxy, it is described as being comparable in size to the Large Magellanic Cloud (LMC), a very small satellite galaxy of our Milky Way seen in the southern hemisphere. Tayna is rapidly making stars at a rate ten times faster than the LMC, and is likely the growing core of what will evolve into a full-sized galaxy.

This faintest ancient galactic find is part of a discovery of 22 young galaxies at ancient times located nearly at the observable horizon of the universe, research that substantially increases in the number of known very distant galaxies.

“The big unanswered question is how and when did the stars and galaxies turn on to end those Dark Ages,” said Green.  “There was a point when they started popping like popcorn.  With Hubble we can go back only so far and can’t see anymore, but the James Webb can go significantly further and see back to the Dark Ages.”

Massive cosmic objects, from single stars to galaxy clusters, bend and focus the light that flows around them with their gravity, acting like giant magnifying glasses. This effect is called gravitational lensing or, when it is detected on tiny patches on the sky, microlensing. Credit: ESA/ATG medialab Read more at: http://phys.org/news/2015-07-astronomers-cosmic-gravity-black-hole-scope.html#jCp
Massive cosmic objects, from single stars to galaxy clusters, bend and focus the light that flows around them with their gravity, acting like giant magnifying glasses. This effect is called gravitational lensing or, when detected on distant plants and faint galaxies, microlensing. (ESA/ATG medialab)

Ironically, Infante and his team were able to find the faintest distant galaxy so far without having it be the hardest to see.  That’s because they were able to use a technique of observing first proposed by Albert Einstein.  As described on the HubbleSite:

The small and faint galaxy was only seen thanks to a natural “magnifying glass” in space. As part of its Frontier Fields program, Hubble observed a massive cluster of galaxies, MACS J0416.1-2403, located roughly 4 billion light-years away and weighing as much as a million billion suns. This giant cluster acts as a powerful natural lens by bending and magnifying the light of far-more-distant objects behind it. Like a zoom lens on a camera, the cluster’s gravity boosts the light of the distant protogalaxy to make it look 20 times brighter than normal. The phenomenon is called gravitational lensing and was proposed by Einstein as part of his General Theory of Relativity.

While gravitational lensing uses a galaxy cluster as its magnifying glass, “microlensing” takes advantage of the same physics but uses a single star in our galaxy as the lens.  That technique is the only known method capable of discovering planets at truly great distances from the Earth. Radial velocity searches look for planets in our immediate galactic neighborhood, up to 100 light years from Earth, transit photometry can potentially detect planets at a distance of hundreds of light-years, but only microlensing can find planets orbiting stars near the center of the galaxy, thousands of light-years away.

And in the spirit of the wonder that microlensing tends to engender, let me leave you with another of those defining astronomical images that are impossible to ignore or forget.

This is the third version of the Hubble Ultra Deep Field, first assembled from 2003-2004 images, upgraded to the Hubble eXtreme Deep Field (XDF) image in 2012 and then enhanced further in 2014 and returned to the original Hubble Ultra Deep Field name.  Both the XDF and the 2014 version capture a patch of sky at the center of the original Hubble Ultra Deep Field.  That initial effort, which looked back in time approximately 13 billion years, picked up many unintentionally microlensed galaxies.

The newer images feature about 5,500 galaxies even within its smaller field of view. The faintest galaxies are one ten-billionth the brightness of what the human eye can see; just imagine that ratio for a single star or a planet.

So while there undoubtedly are an untold numbers of planets in the field, they will remain hidden for a very long time to come.

Hubble Ultra Deep from 2014. using full range of ultraviolet to near infrared, includes some of the most distant galaxies imaged by an optical telescope.
Hubble Ultra Deep Field from 2014. using full range of ultraviolet to near infrared, includes some of the most distant galaxies imaged by an optical telescope.  It is the third iteration of the Hubble Ultra Deep Field image, and combines more than 10 years of Hubble photographs taken of a patch of sky at the center of the original creation. (NASA)
Facebooktwittergoogle_plusredditpinterestlinkedinmail