Regarding matter that has the highest redshifts, do we see such matter in every general direction we look (relative to Earth: up down left right front back)?
It's not possible to see photons from "beyond" the cosmic microwave background (CMB), because (assuming our cosmology is generally correct) the CMB is the result of recombination of electrons with protons in the early universe. Photons from before that era were absorbed in the plasma.
Essentially then, the earliest matter we can see (in photonic terms) is this glowing hot hydrogen, but massively red-shifted so it looks like hydrogen at 3K.
We see the CMB in every direction.
Farthest Stars in Milky Way Might Be Ripped from Another Galaxy
The 11 farthest known stars in our galaxy are located about 300,000 light-years from Earth, well outside the Milky Way's spiral disk. New research by Harvard astronomers shows that half of those stars might have been ripped from another galaxy: the Sagittarius dwarf. Moreover, they are members of a lengthy stream of stars extending one million light-years across space, or 10 times the width of our galaxy.
"The star streams that have been mapped so far are like creeks compared to the giant river of stars we predict will be observed eventually," says lead author Marion Dierickx of the Harvard-Smithsonian Center for Astrophysics (CfA).
The Sagittarius dwarf is one of dozens of mini-galaxies that surround the Milky Way. Over the age of the universe it made several loops around our galaxy. On each passage, the Milky Way's gravitational tides tugged on the smaller galaxy, pulling it apart like taffy.
Dierickx and her PhD advisor, Harvard theorist Avi Loeb, used computer models to simulate the movements of the Sagittarius dwarf over the past 8 billion years. They varied its initial velocity and angle of approach to the Milky Way to determine what best matched current observations.
"The starting speed and approach angle have a big effect on the orbit, just like the speed and angle of a missile launch affects its trajectory," explains Loeb.
At the beginning of the simulation, the Sagittarius dwarf weighed about 10 billion times the mass of our Sun, or about one percent of the Milky Way's mass. Dierickx's calculations showed that over time, the hapless dwarf lost about a third of its stars and a full nine-tenths of its dark matter. This resulted in three distinct streams of stars that reach as far as one million light-years from the Milky Way's center. They stretch all the way out to the edge of the Milky Way halo and display one of the largest structures observable on the sky.
Moreover, five of the 11 most distant stars in our galaxy have positions and velocities that match what you would expect of stars stripped from the Sagittarius dwarf. The other six do not appear to be from Sagittarius, but might have been removed from a different dwarf galaxy.
Mapping projects like the Sloan Digital Sky Survey have charted one of the three streams predicted by these simulations, but not to the full extent that the models suggest. Future instruments like the Large Synoptic Survey Telescope, which will detect much fainter stars across the sky, should be able to identify the other streams.
"More interlopers from Sagittarius are out there just waiting to be found," says Dierickx.
These findings have been accepted for publication in The Astrophysical Journal and are available online.
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
Astronomers find farthest galaxy group identified to date
Bahram Mobasher, a professor of observational astronomy at UC Riverside, is a member of an international team of astronomers that found the farthest galaxy group identified to date. Called EGS77, the group of three galaxies dates to a time when the universe was only 680 million years old.
Illustration of the EGS77 galaxy group shows the galaxies surrounded by overlapping bubbles of hydrogen ionized by ultraviolet light from their stars. (NASA's Goddard Space Flight Center)
While more distant galaxies have been observed, EGS77 is the farthest galaxy group to date showing the specific wavelengths of far-ultraviolet light revealed by reionization, the era when light from the first stars changed the nature of hydrogen throughout the universe.
“Our universe went through a period of dark ages when it was 380,000 years old that lasted for 600
million years,” Mobasher said. “During this time clouds of molecular hydrogen condensed and formed the very first generation of stars. These stars were very bright and emitted high-energy ultra-violet radiation, which resulted in ionizing the hydrogen atoms around them.”
The nature, space density, and concentration of the objects responsible for the ionization of the universe are being intensively studied today.
“What we found was the first evidence of a group of galaxies when the universe came out of this period of dark ages — when it was one billion years old,” Mobasher said.
The findings were presented on Jan. 5 at the 235th meeting of the American Astronomical Society by James Rhoads at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He explained that the hydrogen atoms that filled the early universe attenuated ultraviolet light, which blocked astronomers’ view of early galaxies.
“EGS77 is the first galaxy group caught in the act of clearing out this cosmic fog,” said Rhoads, who served as principal investigator of the Cosmic Deep And Wide Narrowband, or Cosmic DAWN, survey. EGS77 was discovered as part of this survey.
Mobasher, a co-founder of the DAWN survey with Rhoads and Sangeeta Malhotra of the Goddard Space Flight Center, was involved in planning and interpreting spectroscopic observations.
A paper describing the findings has been submitted to The Astrophysical Journal.
This is a real-time indicator of Voyagers' distance from Earth in astronomical units (AU) and either miles (mi) or kilometers (km).
Note: Because Earth moves around the sun faster than Voyager 1 is speeding away from the inner solar system, the distance between Earth and the spacecraft actually decreases at certain times of year.
This is a real-time indicator of Voyagers' straight-line distance from the sun in astronomical units (AU) and either miles (mi) or kilometers (km).
The elapsed time it takes for light (or radio signals) to travel between the Earth and a celestial object.
Note: Because Earth moves around the Sun faster than Voyager 1 or Voyager 2 is traveling from Earth, the one-way light time between Earth and each spacecraft actually decreases at certain times of the year.
This meter depicts the dramatic changes in readings by Voyager’s cosmic ray instrument. The instrument detected a dip in the levels of charged particles that originate from inside our heliosphere(green), and rise in the levels of cosmic rays – charged particles that originate from stars other than our sun(orange). These data had suggested that Voyager 1 entered interstellar space on August 25, 2012, when the inside particles(green) dipped closer to 0.0 and the outside particles(orange) rose above 2.0.
|Instrument||Voyager 1||Voyager 2|
|Cosmic Ray Subsystem (CRS)||ON||ON|
|Low-Energy Charged Particles (LECP)||ON||ON|
|Plasma Wave Subsystem (PWS)||ON||ON|
|Plasma Science (PLS)||Off because of degraded performance (Feb. 1, 2007)||ON|
|Imaging Science Subsystem (ISS)||Wide-angle and narrow-angle cameras off to save power (Feb. 14, 1990)||Wide-angle and narrow angle cameras off to save power (Oct. 10 and Dec. 5, 1989)|
|Infrared Interferometer Spectrometer and Radiometer (IRIS)||Off to save power (June 3, 1998)||Off to save power (Feb. 1, 2007)|
|Photopolarimeter Subsystem (PPS)||Off because of degraded performance (Jan. 29, 1980)||Off because of degraded performance (April 3, 1991)|
|Planetary Radio Astronomy (PRA)||Off to save power (Jan. 15, 2008)||Off to save power (Feb. 21, 2008)|
|Ultraviolet Spectrometer (UVS)||Off to save power (April 19, 2016)||Off to save power (Nov. 12, 1998)|
Where are the Voyagers now?
To learn more about Voyager, zoom in and give the spacecraft a spin. View the full interactive experience at Eyes on the Solar System. Credit: NASA/JPL-Caltech
Pinning Down the Distance to the Farthest Galaxy Ever Observed
The first few hundreds of millions of years (Myrs) of the universe include some of the most dramatic changes it has undergone, transforming from a near uniform distribution of gas into a diverse landscape of the first stars and galaxies. The early universe, characterized by an enormous abundance of pristine gas and by a dearth of massive structures looks quite unlike the universe today. If you were an observer peering into the young cosmos, you would be able to see very little around yourself, as the abundant neutral gas blocked most light from passing through and reaching you. However, the young stars in these early galaxies sent out high-energy photons throughout the expanse of gas, which ionized abundant hydrogen, eventually making the intergalactic medium transparent. The formation of the first galaxies, as well as their important role in reionizing the universe , is poorly understood because these galaxies appear faint owing to their distance, and are only visible in infrared wavelengths and beyond, altogether making them difficult to observe, especially from the ground.
The most distant galaxy known to date is called GN-z11. First discovered over four years ago within the GOODS-North field , this most distant galaxy is located all the way at a redshift of nearly z = 11, hence the name (note that a redshift of z = 11 corresponds to a distance of over 32 billion light years). The light we observe from this galaxy corresponds to a time roughly 400 Myrs after the Big Bang, right at the onset of the reionization period. The discovery of such a galaxy provides an extraordinary opportunity to unravel the processes of galaxy evolution during one of the most poorly understood epochs of the universe. In today’s astrobite, we explore a recent work which firmly establishes GN-z11 as the most distant galaxy currently known and uniquely investigates some of its physical characteristics.
Figure 1: Galaxy GN-z11, the most distant galaxy ever observed, is shown within the GOODS-North survey field where it was originally discovered with the Hubble Space Telescope. This galaxy is shown in red, reflecting that its light is detected in the infrared due to cosmological redshift. Credit: NASA/ESA P. Oesch et al. (2016).
How to confirm a distant galaxy
When carrying out surveys in which several thousands of galaxies are observed, a standard practice is to first extract photometry for each source in every available filter, and then remarkably, use this photometry to estimate each source’s respective redshift. Once the redshift is known, observed quantities (like apparent magnitude) can be converted into physical quantities (like luminosity). These “photometric redshifts” are quick to obtain but not nearly as reliable as spectroscopic redshifts , which can only be measured from a high-quality spectrum of a given galaxy spectroscopic observations always require far more observing time than imaging per galaxy, since the observed light is dispersed across the detector.
In this work, a team of astronomers led by Linhua Jiang of Peking University utilized the unique capabilities of the Keck-1 telescope on Manuakea, Hawaii (the largest infrared-capable telescope) to obtain the first detailed spectroscopic observations of GN-z11. Previously observed with both the Hubble Space Telescope and the Spitzer Space Telescope, a different team derived a photometric redshift and a “ grism ” redshift for the same source of z
11. With the new observations from Jiang’s team, which required over 9 hours of total exposure time , the redshift of this galaxy can be firmly established at z = 10.957 through the detection of three emission lines, one of which is significant above the 5-sigma level (generically corresponding to a false positive chance of 1 in 3.5 million). Figure 2 shows two of the emission lines detected in both the one and two-dimensional spectra of GN-z11.
Figure 2: Panels (a) and (b) depict the ordinary and smoothed versions of the two-dimensional spectrum of GN-z11, where the vertical dimension corresponds to the position of the slit on the mask while the horizontal dimension corresponds to wavelength. Panels (c) and (d) depict the corresponding one-dimensional spectra. The emission lines are circled in yellow in the upper panels, and the names of the identified spectral features are given in the bottom panels. The grey filled region in the upper panels depicts the 1-sigma uncertainty these lines are detected at 2.6 and 5.3-sigma respectively. Figure 2 in the original work.
Inferred properties of the most distant galaxy known
As stated above, with the redshift established, apparent properties can be converted into physical quantities. In brief, the common method for estimating the physical properties of galaxies is done through comparing its observed spectral energy distribution ( SED constrained by either photometry or spectroscopy, or both) with synthetic spectral energy distributions (i.e. models) of galaxies in which all of the properties are known. In this case, the authors compare simple synthetic SED with the existing Hubble and Spitzer photometry to measure three properties of the GN-z11: its dust reddening , age, and its stellar mass. The best-fit model is shown below in Figure 3.
Figure 3: Demonstration of modeling the SED of GN-z11. Red data points spanning the NIR to mid-IR correspond to the observed HST, ground-based, and Spitzer photometry taken from the literature. The grey SED, corresponding to a galaxy located at z = 10.957, provides a significantly better fit to the data compared to the blue SED, which corresponds to a galaxy at z = 3.558, a plausible solution if the observed emission lines were identified incorrectly. The physical properties of GN-z11 are thus derived from the grey SED. Panel (a) from Extended Data Figure 4 in the original work.
Unsurprisingly, the derived dust reddening is consistent with zero, meaning there is little dust present in this galaxy – this is expected, since dust content is built up from generations of stars completing their evolution cycles, which GN-z11 should not yet have experienced. The age, although uncertain due to the sparse sampling of the SED, is also reported to be very young, clocking in at less than 100 Myr. Lastly, the stellar mass is found to be a little more than a billion solar masses, roughly one sixtieth of the mass of the Milky Way. However, the Milky Way as we know it has had the entire history of the universe to build this much mass in stars, over 13 billion years, whereas GN-z11 has achieved its mass in only a few hundreds of Myr. This implies that the build-up of stars in GN-z11 must have been extraordinarily rapid.
Further information is revealed from the new spectrum of GN-z11. The particular spectral line detected at greater than 5-sigma (CIII]) is sensitive to the electron density of the material from which it was emitted. The width of this line, shown in Figure 2 above, suggests a very dense interstellar medium within GN-z11, and may indicate that GN-z11 hosts an active galactic nucleus .
The future of high-z galaxy studies
With new observatories on the horizon specializing in infrared observations, such as the Euclid mission , the Nancy Grace Roman Space Telescope , the James Webb Space Telescope , we are on the cusp of exploring the realm of reioniziation and the first billion years of the universe in ever greater detail. While the current record holder for the most distant galaxy is GN-z11, we should expect to find many more galaxies at similar distances with these new facilities through their combination of field of view (especially Euclid’s and Roman’s), and resolving power (one of JWST’s primary features). For the time being, GN-z11 has revealed a tremendous amount of information about the early universe, and the confirmation of its distance is an encouraging testament to the methods astronomers have developed for finding such rare objects in the vast cosmos.
Maturity of Farthest Galaxy Cluster Surprises Astronomers
CALGARY, ALBERTA--A ghostly blue blob amid a swarm of red dots in a new cosmic image is the superhot intergalactic gas permeating the space within the most distant cluster of galaxies found to date.
Located nearly 10 billion light-years away, Cluster XMMXCS 2215-1738 is being hailed by its discoverers as a tantalizing glimpse of what galaxy clusters were like at their earliest stages of formation.
Individual galaxies have been detected at greater distances. But the newly discovered cluster contains several hundred galaxies bound together by mutual gravitational attraction.
The finding was announced here this week at the 208th meeting of the American Astronomical Society.
A light-year is the distance that light can travel in a year, so the light from this cluster took almost 10 billion years to reach us. Since the universe is thought to be 13.7 billion years old, the record-setting cluster must have formed when the universe was relatively young.
"Yet this distant cluster appears to be full of old galaxies," discovery team member Adam Stanford noted with amazement.
Stanford and his colleagues said the total mass of the cluster is enough to contain 500 trillion stars comparable in mass to our Sun. That's a surprising stellar mass for a galaxy cluster to have achieved at such an early era in the evolution of the universe, said Stanford, a researcher at the University of California, Davis, and at Lawrence Livermore National Laboratory.
Stanford and the other members of the XMM Cluster Survey, an international team of astronomers, made their discovery by combining X-ray observations from the European X-ray Multi Mirror (XMM) Newton satellite with optical observations using the 10-meter W.M. Keck telescope on Mauna Kea, Hawaii.
Intergalactic gas in the record-setting cluster glows with powerful x-ray emissions at a temperature of 10 million degrees, said team member Robert Nichol, from the University of Portsmouth, England. That's what made the detection of this distant cluster possible, says Nichol. It also makes this a "hot" find in every sense of the word, since this is the hottest cluster yet found at an extreme distance.
But it doesn't end there. Within the patch of the universe covered by the Cluster Survey, Nichol says they can see hints of more tan 1,600 additional galaxy clusters waiting to be confirmed and studied in detail.
"The total number of clusters depends on the amount of dark matter there is," Nichol said. "So this will give us a wonderful measure of how much dark matter there is in the universe."
Dark matter is mysterious stuff that astronomers say must exist, based on the fact that there is not enough regular matter in galaxies to keep them from flying apart.
Extremely distant galaxy clusters like these, Stanford said, give astronomers a great chance "to study galaxy formation by looking at what they were like in the earlier stages of their lifespan."
Stanford is also a team member for a separate galaxy-cluster study that presented its results at the same meeting. Co-led by Mark Brodwin of NASA's Jet Propulsion Laboratory in Pasadena, this team used the Spitzer Space Telescope to discover a total of almost 300 galaxy clusters and groups (galaxy "groups" contain far fewer members than the average galaxy cluster).
Nearly 100 of their finds are at immense distances of over 8 billion light-years.
"The Spitzer Space Telescope sees the thermal radiation of these galaxy clusters at infrared wavelengths," Brodwin explained. "Now, we'll be able to use this large sample of clusters as a laboratory to study the evolution of galaxies."
GN-z11: Astronomers Discover Farthest Galaxy Yet
GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the Big Bang. Image credit: NASA / ESA / P. Oesch, Yale University / G. Brammer, STScI / P. van Dokkum, Yale University / G. Illingworth, University of California, Santa Cruz.
This galaxy, dubbed GN-z11, is located in the direction of the constellation Ursa Major.
It is approximately 25 times smaller than the Milky Way Galaxy and has just 1% of our galaxy’s mass in stars.
GN-z11 is the subject of a study accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“We see GN-z11 at a time when the Universe was only 3% of its current age,” said Yale University astronomer Dr. Pascal Oesch, lead author on the study.
Dr. Oesch and co-authors used Hubble’s Wide Field Camera 3 to precisely measure the distance to the galaxy spectroscopically by splitting the light into its component colors.
“We pushed Hubble to its limits to get the spectroscopic data needed to determine the galaxy’s redshift, a measure of its distance from Earth,” said co-author Prof. Garth Illingworth, of the University of California, Santa Cruz.
This graphic shows a timeline of the Universe, stretching from the present day (left) all the way back to the Big Bang (right). The position of GN-z11 is shown not far from where the first stars began to form. The previous record holder’s position is also identified. Image credit: NASA / ESA / A. Field, STScI.
Before the astronomers determined the distance for GN-z11, the most distant galaxy measured spectroscopically – EGSY8p7 – had a redshift of 8.68 (13.2 billion years in the past).
GN-z11 has a redshift of 11.1, nearly 200 million years closer to the Big Bang.
“It’s amazing that a galaxy so massive existed only 200 million to 300 million years after the very first stars started to form,” Prof. Illingworth said.
“It takes really fast growth, producing stars at a huge rate, to have formed a galaxy that is a billion solar masses so soon.”
Ask Ethan: How Far Is The Edge Of The Universe From The Farthest Galaxy?
Our deepest galaxy surveys can reveal objects tens of billions of light years away, but even with . [+] ideal technology, there will be a large distance gap between the farthest galaxy and the Big Bang.
Sloan Digital Sky Survey (SDSS)
When we look out into the Universe, there's light everywhere we can see, for as far as our telescopes are capable of looking. But at some point, there's a limit to what we'll encounter. One limit is set by the cosmic structure that forms in the Universe: we can only see the stars, galaxies, etc., as long as they emit light. Without that ingredient, our telescopes can't detect anything. But another limit, if we can use astronomy to go beyond starlight, is the limit of how much of the Universe is accessible to us since the Big Bang. These two values might not have much to do with one another, and that's what Oleg Pestovsky wants to know!
Why is the redshift of CMB . around 1,000, while the highest redshift for any galaxy we have observed is 11?
The first thing we need to think about is exactly what happens in our Universe, moving forward, from the moment of the Big Bang.
The observable Universe might be 46 billion light years in all directions from our point of view, . [+] but there's certainly more, unobservable Universe, perhaps even an infinite amount, just like ours beyond that.
Frédéric MICHEL and Andrew Z. Colvin, annotated by E. Siegel
The full suite of all we know, see, observe and interact with is what we'll call the "Observable Universe." Beyond what we can see, there's very likely more Universe out there, and as time goes on, we'll be able to see more and more of it, as light from more distant objects finally reaches us after a cosmic journey taking billions of years. Seeing what we do in the Universe (and not more, and not less) is possible because of a combination of three things:
- The fact that it's been a finite amount of time, 13.8 billion years, since the Big Bang,
- The fact that the speed of light, the maximum speed that any signal or particle can travel in the Universe, is finite and constant,
- And the fact that the fabric of space itself has been stretching and expanding ever since the Big Bang occurred.
The timeline of our observable Universe's history.
What we see today is the result of those three conditions, combined with the initial distribution of matter and energy, operating under the laws of physics for the entire history of our Universe. If we want to know what the Universe was like at any earlier time, all we need to do is observe what the Universe is like today, measure all the relevant parameters, and calculate what it was like in the past. There's a lot we have to observe and measure to get there, but Einstein's equations, difficult though they are, are at least straightforward. (The derived results are two equations known as the Friedmann equations, and solving them is a task every graduate student in cosmology becomes intimately familiar with.) And, quite honestly, we've made some incredible measurements about the Universe.
Looking towards the north pole of the Milky Way galaxy, we can see out into the depths of space. . [+] What's mapped in this image are hundreds of thousands of galaxies, where each pixel in the image is a unique galaxy.
We know how fast it's expanding today. We know what the matter density is everywhere we look. We know how much structure forms on all different scales, from globular clusters to dwarf galaxies to larger galaxies to groups and clusters and large-scale filaments. We know how much of the Universe is normal matter, dark matter, dark energy, as well as much smaller components like neutrinos, radiation and even black holes. And just from that information, extrapolating backwards in time, we can decipher both how big the Universe was and how fast it was expanding at any point in its cosmic history.
A graph of the size/scale of the observable Universe vs. the passage of cosmic time. This is . [+] displayed on a log-log scale, with a few major size/time milestones identified.
Today, our observable Universe extends for approximately 46.1 billion light years in all directions from where we are. That's the distance that if, at the instant of the Big Bang, the original location-in-space of an imaginary particle traveling at the speed of light would be at today if it were to reach us right now, 13.8 billion years later. In principle, that's where any gravitational waves left over from cosmic inflation — the state prior to the Big Bang that set it up and provided its initial conditions — would originate from.
Gravitational waves generated by cosmic inflation are the farthest signal back in time humanity can . [+] conceive of potentially detecting, which originate from the end of cosmic inflation and the very beginning of the hot Big Bang.
National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program modifications by E. Siegel
But there are other signals left over from the Universe as well. When the Universe was about 380,000 years old, the leftover radiation from the Big Bang stopped scattering off of free, charged particles as they formed neutral atoms. These photons, once neutral atoms form, continue to redshift with the expanding Universe, and can be seen with a microwave or radio telescope/antenna today. But because of how rapidly the Universe expanded back in the earliest stages, the "surface" we see this leftover glow at — the cosmic microwave background — is already only 45.2 billion light years away. The distance from the beginning of the Universe to where the Universe is at 380,000 years of age is already 900 million light years!
The light we perceive as the cosmic microwave background is actually leftover photons from the Big . [+] Bang, released at the instant they last scattered off of free electrons. Although that light travels for 13.8 billion years before reaching us, the expansion of space causes that location to be, at present, 45.2 billion light years away.
E.M. Huff, the SDSS-III team and the South Pole Telescope team graphic by Zosia Rostomian
It's much, much longer than that until we find the most distant galaxy ever discovered in the Universe. While simulations and calculations indicate that the very first stars may have formed when the Universe was between 50 and 100 million years old, and the very first galaxies at around 200 million years, we haven't been able to see back that far just yet. (Although, hopefully, with the James Webb Space Telescope launching next year, we soon will!) The current cosmic record-holder, shown below, is a galaxy from when the Universe was 400 million years old: just 3% of its present age. However, that galaxy, GN-z11, is only located 32 billion light years away: some 14 billion light years from the "edge" of the observable Universe.
The most distant galaxy ever found: GN-z11, in the GOODS-N field as imaged deeply (but not the . [+] deepest-ever) by Hubble.
NASA, ESA, and P. Oesch (Yale University)
The reason for this? The expansion rate has been dropping in a tremendous fashion over time. At the time galaxy Gz-11 existed in the state we see it, the Universe was expanding 20 times faster than it is today. When the cosmic microwave background was emitted, the Universe was expanding 20,000 times faster than it is today. And at the moment of the Big Bang, to the best of our knowledge, the Universe was expanding some 10^36 times faster, or 1,000,000,000,000,000,000,000,000,000,000,000,000 times faster than it is today. The Universe's expansion rate has been slowing down tremendously over time.
This is incredibly good for us! The balance between the initial expansion rate and the total amount of energy in the Universe in all its forms is perfectly balanced, to the limits of the quality of our observations. If the Universe had even slightly too much matter or radiation in the early stages, it would have recollapsed billions of years ago, and we wouldn't exist. If the Universe had slightly too little matter or radiation early on, it would have expanded too quickly for particles to find one another and even form atoms, much less complex structures like galaxies, stars, planets and humans. The cosmic story that the Universe tells to us is one of extraordinary balance, and one where we actually get to exist.
The intricate balance between the expansion rate and the total density in the Universe is so . [+] precarious that even a 0.00000000001% difference in either direction would render the Universe completely inhospitable to any life, stars, or potentially even molecules existing at any point in time.
Ned Wright’s Cosmology tutorial
If our current best theories are correct, the first true galaxies will have formed at some point between around 120 and 210 million years of age. That corresponds to a distance from us of between 37 and 35 billion light years, placing the distance from the farthest galaxy of all to the edge of the observable Universe at 9-to-11 billion light years today. That's incredibly far, and points to one incredible fact: the Universe was expanding extremely rapidly in the early stages, and expands at a much slower rate today. That first 1% of the Universe's age is responsible for approximately 20% of the Universe's total expansion!
The history of our Universe is filled with a number of fantastic events, but since inflation ended . [+] and the hot Big Bang occurred, the expansion rate has been dropping precipitously, and slowing its rate of descent as the density continues to drop.
Bock et al. (2006, astro-ph/0604101) modifications by E. Siegel
The expansion of the Universe is what's stretched the light's wavelength (and caused the "redshift" we see), and that rapid expansion is why there's such a difference between the cosmic microwave background and the farthest galaxy. But the size of the Universe today is evidence of something else incredible: the incredible effects that the progression of time has. As time goes on, the Universe will continue to expand farther and farther, and by time it's around ten times its current age, distances will have expanded so much that no galaxies beyond our local group will be visible, even with the equivalent of the Hubble Space Telescope. Enjoy all we can see today about the great variety of what's present on all cosmic scales. It won't be around forever!
Research Box Title
More than halfway across the universe, an enormous blue star nicknamed Icarus is the farthest individual star ever seen. Normally, it would be much too faint to view, even with the world’s largest telescopes. But through a quirk of nature that tremendously amplifies the star’s feeble glow, astronomers using NASA’s Hubble Space Telescope were able to pinpoint this faraway star and set a new distance record. They also used Icarus to test one theory of dark matter, and to probe the make-up of a foreground galaxy cluster.
The star, harbored in a very distant spiral galaxy, is so far away that its light has taken 9 billion years to reach Earth. It appears to us as it did when the universe was about 30 percent of its current age.
The discovery of Icarus through gravitational lensing has initiated a new way for astronomers to study individual stars in distant galaxies. These observations provide a rare, detailed look at how stars evolve, especially the most luminous stars.
“This is the first time we’re seeing a magnified, individual star,” explained former University of California at Berkeley postdoc and study leader Patrick Kelly now of the University of Minnesota, Twin Cities. “You can see individual galaxies out there, but this star is at least 100 times farther away than the next individual star we can study, except for supernova explosions.”
Gravity as a Natural Cosmic Lens
The cosmic quirk that makes this star visible is a phenomenon called “gravitational lensing.” Gravity from a foreground, massive cluster of galaxies acts as a natural lens in space, bending and amplifying light. Sometimes light from a single background object appears as multiple images. The light can be highly magnified, making extremely faint and distant objects bright enough to see.
In the case of Icarus, a natural “magnifying glass” is created by a galaxy cluster called MACS J1149+2223. Located about 5 billion light-years from Earth, this massive cluster of galaxies sits between the Earth and the galaxy that contains the distant star. By combining the strength of this gravitational lens with Hubble’s exquisite resolution and sensitivity, astronomers can see and study Icarus.
The team — including Jose Diego of the Instituto de Física de Cantabria, Spain, and Steven Rodney of the University of South Carolina, Columbia — dubbed the star “Icarus,“ after the Greek mythological character who flew too near the Sun on wings of feathers and wax that melted. (Its official name is MACS J1149+2223 Lensed Star 1.) Much like Icarus, the background star had only fleeting glory as seen from Earth: It momentarily skyrocketed to 2,000 times its true brightness when temporarily magnified.
Models suggest that the tremendous brightening was probably from the gravitational amplification of a star, similar in mass to the Sun, in the foreground galaxy cluster when the star moved in front of Icarus. The star’s light is usually magnified by about 600 times due to the foreground cluster’s mass.
The team had been using Hubble to monitor a supernova in the far-distant spiral galaxy when, in 2016, they spotted a new point of light not far from the magnified supernova. From the position of the new source, they inferred that it should be much more highly magnified than the supernova.
When they analyzed the colors of the light coming from this object, they discovered it was a blue supergiant star. This type of star is much larger, more massive, hotter, and possibly hundreds of thousands of times intrinsically brighter than our Sun. But at this distance, it would still be too far away to see without the amplification of gravitational lensing, even for Hubble.
How did Kelly and his team know Icarus was not another supernova? “The source isn’t getting hotter it’s not exploding. The light is just being magnified,” said Kelly. “And that’s what you expect from gravitational lensing.”
Looking for Dark Matter
Detecting the amplification of a single, pinpoint background star provided a unique opportunity to test the nature of dark matter in the cluster. Dark matter is an invisible material that makes up most of the universe’s mass.
By probing what’s floating around in the foreground cluster, scientists were able to test one theory that dark matter might be made up mostly of a huge number of primordial black holes formed in the birth of the universe with masses tens of times larger than the Sun. The results of this unique test disfavor that hypothesis, because light fluctuations from the background star, monitored with Hubble for 13 years, would have looked different if there were a swarm of intervening black holes.
When NASA's James Webb Space Telescope is launched, astronomers expect to find many more stars like Icarus. Webb's extraordinary sensitivity will allow measurement of even more details, including whether these distant stars are rotating. Such magnified stars may even be found to be fairly common.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
Credits:NASA, ESA, and P. Kelly (University of Minnesota)
Farthest Known Supermassive Black Hole Discovered
Scientists have uncovered a rare relic from the early universe: the farthest known supermassive black hole.
This matter-eating beast is 800 million times the mass of our Sun, which is astonishingly large for its young age. Researchers report the find in the journal Nature.
"This black hole grew far larger than we expected in only 690 million years after the Big Bang, which challenges our theories about how black holes form," said study co-author Daniel Stern of NASA's Jet Propulsion Laboratory in Pasadena, California.
Astronomers combined data from NASA's Wide-field Infrared Survey Explorer (WISE) with ground-based surveys to identify potential distant objects to study, then followed up with Carnegie Observatories' Magellan telescopes in Chile. Carnegie astronomer Eduardo Bañados led the effort to identify candidates out of the hundreds of millions of objects WISE found that would be worthy of follow-up with Magellan.
For black holes to become so large in the early universe, astronomers speculate there must have been special conditions to allow rapid growth -- but the underlying reason remains mysterious.
The newly found black hole is voraciously devouring material at the center of a galaxy -- a phenomenon called a quasar. This quasar is especially interesting because it comes from a time when the universe was just beginning to emerge from its dark ages. The discovery will provide fundamental information about the universe when it was only 5 percent of its current age.
"Quasars are among the brightest and most distant known celestial objects and are crucial to understanding the early universe," said co-author Bram Venemans of the Max Planck Institute for Astronomy in Germany.
The universe began in a hot soup of particles that rapidly spread apart in a period called inflation. About 400,000 years after the Big Bang, these particles cooled and coalesced into neutral hydrogen gas. But the universe stayed dark, without any luminous sources, until gravity condensed matter into the first stars and galaxies. The energy released by these ancient galaxies caused the neutral hydrogen to get excited and ionize, or lose an electron. The gas has remained in that state since that time. Once the universe became reionized, photons could travel freely throughout space. This is the point at which the universe became transparent to light.
Much of the hydrogen surrounding the newly discovered quasar is neutral. That means the quasar is not only the most distant -- it is also the only example we have that can be seen before the universe became reionized.
"It was the universe's last major transition and one of the current frontiers of astrophysics," Bañados said.
The quasar's distance is determined by what's called its redshift, a measurement of how much the wavelength of its light is stretched by the expansion of the universe before reaching Earth. The higher the redshift, the greater the distance, and the farther back astronomers are looking in time when they observe the object. This newly discovered quasar has a redshift of 7.54, based on the detection of ionized carbon emissions from the galaxy that hosts the massive black hole. That means it took more than 13 billion years for the light from the quasar to reach us.
Scientists predict the sky contains between 20 and 100 quasars as bright and as distant as this quasar. Astronomers look forward to the European Space Agency's Euclid mission, which has significant NASA participation, and NASA's Wide-field Infrared Survey Telescope (WFIRST) mission, to find more such distant objects.
"With several next-generation, even-more-sensitive facilities currently being built, we can expect many exciting discoveries in the very early universe in the coming years," Stern said.