Hubble's view of NGC 4214, Canes Venatici (The Hunting Dogs). Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration
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Lots of activity taking place inside NGC 4214, and Hubble has peered inside this dwarf galaxy to see stars in all stages of their evolution, as well as gas clouds with huge cavities blown out by stellar winds. Wow! Also visible are bright stellar clusters and complex patterns of glowing hydrogen, some forming a candy-cane-like structure in the upper right of this optical and near-infrared image. NGC 4214 is located in the constellation of Canes Venatici (The Hunting Dogs), about 10 million light-years away. Hubble scientists say this galaxy is an ideal laboratory to research the triggers of star formation and evolution.
Observations of this dwarf galaxy have also revealed clusters of much older red supergiant stars. Additional older stars can be seen dotted all across the galaxy. The variety of stars at different stages in their evolution indicates that the recent and ongoing starburst periods are not the first, and the galaxy’s abundant supply of hydrogen means that star formation will continue into the future.
The Meathook Galaxy, or NGC 2442, has a dramatically lopsided shape. One spiral arm is tightly folded in on itself and host to a recent supernova, while the other, dotted with recent star formation, extends far out from the nucleus. The MPG/ESO 2.2-metre telescope and the NASA/ESA Hubble Space Telescope have captured two contrasting views of this asymmetric spiral galaxy.
The Meathook Galaxy, or NGC 2442, in the southern constellation of Volans (The Flying Fish), is easily recognised for its asymmetric spiral arms. The galaxy’s lopsided appearance is thought to be due to gravitational interactions with another galaxy at some point in its history — though astronomers have not so far been able to positively identify the culprit.
This broad view, taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at La Silla, Chile, very clearly shows the double hook shape that gives the galaxy its nickname. This image also captures several other galaxies close to NGC 2442 as well as many more remote galaxies that form a rich backdrop. Although the Wide Field Imager, on the ground, cannot approach the sharpness of images from Hubble in space, it can cover a much bigger section of sky in a single exposure. The two tools often provide complementary information to astronomers.
This close-up Hubble view of the Meathook Galaxy (NGC 2442) focuses on the more compact of its two asymmetric spiral arms as well as the central regions. The spiral arm was the location of a supernova that exploded in 1999. These observations were made in 2006 in order to study the aftermath of this supernova. Ground-based data from MPG/ESO 2.2-metre telescope were used to fill out parts of the edges of this image. Credit: NASA/ESA and ESO
A close-up image from the NASA/ESA Hubble Space Telescope (eso1115b) focuses on the galaxy’s nucleus and the more compact of its two spiral arms. In 1999, a massive star at the end of its life exploded in this arm in a supernova. By comparing older ground-based observations, previous Hubble images made in 2001, and these shots taken in late 2006, astronomers have been able to study in detail what happened to the star in its dying moments. By the time of this image the supernova itself had faded and is not visible.
ESO’s observations also highlight the other end of the life cycle of stars from Hubble. Dotted across much of the galaxy, and particularly in the longer of the two spiral arms, are patches of pink and red. This colour comes from hydrogen gas in star-forming regions: as the powerful radiation of new-born stars excites the gas in the clouds they formed from, it glows a bright shade of red.
The interaction with another galaxy that gave the Meathook Galaxy its unusual asymmetric shape is also likely to have been the trigger of this recent episode of star formation. The same tidal forces that deformed the galaxy disrupted clouds of gas and triggered their gravitational collapse.
Faint dust plumes bookend asteroid (596) Scheila, which is overexposed in this composite. Visible and ultraviolet images from Swift's UVOT (circled) are merged with a Digital Sky Survey image of the same region. The UVOT images were acquired on Dec. 15, 2010, when the asteroid was about 232 million miles from Earth. Credit: NASA/Swift/DSS/D. Bodewits (UMD)
Asteroid or comet? That was the question astronomers were asking after an asteroid named Scheila had unexpectedly brightened, and seemingly sprouted a tail and coma. But follow-up observations by the Swift satellite and the Hubble Space Telescope show that these changes likely occurred after Scheila was struck by a much smaller asteroid.
“Collisions between asteroids create rock fragments, from fine dust to huge boulders, that impact planets and their moons,” said Dennis Bodewits, an astronomer at the University of Maryland in College Park and lead author of the Swift study. “Yet this is the first time we’ve been able to catch one just weeks after the smash-up, long before the evidence fades away.”
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On Dec. 11, 2010, images from the University of Arizona’s Catalina Sky Survey, a project of NASA’s Near Earth Object Observations Program, revealed the Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey’s archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.
Three days after the outburst was announced, Swift’s Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl (OH) and hydrogen (H). But none of the emissions most commonly identified in comets — such as hydroxyl or cyanogen (CN) — showed up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject the idea that Scheila was actually a comet and that exposed ice accounted for the brightening.
Hubble observed the asteroid’s fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011. Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight.
The science teams from the two space observatories found the observations were best explained by a collision with a small asteroid impacting Scheila’s surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn’t have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust–equivalent to nearly twice the mass of the Empire State Building.
The Hubble Space Telescope imaged (596) Scheila on Dec. 27, 2010, when the asteroid was about 218 million miles away. Scheila is overexposed in this image to reveal the faint dust features. The asteroid is surrounded by a C-shaped cloud of particles and displays a linear dust tail in this visible-light picture acquired by Hubble's Wide Field Camera 3. Because Hubble tracked the asteroid during the exposure, the star images are trailed. Credit: NASA/ESA/D. Jewitt (UCLA)
“The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter,” said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, unlike its 2009 observations of P/2010 A2, the first identified asteroid collision.
Scheila is approximately 113 km (70 miles) across and orbits the sun every five years.
“The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA’s UMD-led Deep Impact mission,” said co-author Michael Kelley, also at the University of Maryland. “Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila’s interior shows that it’s entirely unlike comets.”
The studies will appear in the May 20 edition of The Astrophysical Journal Letters.
A new Hubble image of the Messier 5 cluster. Credit: ESA/Hubble & NASA
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This is just plain pretty. You’re looking at some of the oldest stars in the Universe. This new Hubble image of the globular cluster Messier 5 shows this giant huddle of stars, which is one of the oldest clusters in the Milky Way. Astronomers say the majority of M5’s stars formed more than 12 billion years ago. But there are some new and blue stars among the mix, adding some vitality and color to this ancient bunch.
Stars in globular clusters form in the same stellar nursery and grow old together. The most massive stars age quickly, exhausting their fuel supply in less than a million years, and end their lives in spectacular supernovae explosions. This process should have left the ancient cluster Messier 5 with only old, low-mass stars, which, as they have aged and cooled, have become red giants, while the oldest stars have evolved even further into blue horizontal branch stars.
Yet astronomers have spotted many young, blue stars in this cluster, hiding among the much more luminous ancient stars. Astronomers think that these laggard youngsters, called blue stragglers, were created either by stellar collisions or by the transfer of mass between binary stars. Such events are easy to imagine in densely populated globular clusters, in which up to a few million stars are tightly packed together.
Messier 5 lies at a distance of about 25 000 light-years in the constellation of Serpens (The Snake). This image was taken with Wide Field Channel of Hubble’s Advanced Camera for Surveys.
Spiral galaxy arms may carry stars along with them, suggests new study
There’s a new concept in the works regarding the evolution of galactic arms and how they move across the structure of spiral galaxies. Robert Grand, a postgraduate student at University College London’s Mullard Space Science Laboratory, used new computer modeling to suggest that these signature features of spiral galaxies – including our own Milky Way – evolve in different ways than previously thought.
The currently accepted theory is as spiral galaxies rotate, the “arms” are actually transient structures that move across the flattened disc of stars surrounding the galactic bulge, yet don’t directly affect the movement of the individual stars themselves. This would work in much the same way as a “wave” goes across a crowd at a stadium event. The wave moves, but the individual people do not move along with it – rather, they stay seated after it has passed.
However when Grand researched this suggested motion using computer models of galaxies, he and his colleagues found that this was not what tended to happen. Instead the stars actually moved along with the arms, rather than maintaining their positions.
Also it was observed in these models that the arms themselves are not permanent features, but rather break up and reform over the course of 80 to 100 million years. Grand suggests that this may be due to the powerful gravitational shear forces generated by the spinning of the galaxy.
“We simulated the evolution of spiral arms for a galaxy with five million stars over a period of 6 billion years. We found that stars are able to migrate much more efficiently than anyone previously thought. The stars are trapped and move along the arm by their gravitational influence, but we think that eventually the arm breaks up due to the shear forces.”
– Robert Grand
Snapshots of face-on view of a simulated disc galaxy.
The computer models also showed that the stars along the leading edge of the arms tended to move inwards toward the galactic center while the stars lining the trailing ends were carried to the outer edge of the galaxy.
Since it takes hundreds of millions of years for a spiral galaxy to complete even just one single rotation, observing their evolution and morphology is impossible to do in real time. Researchers like Grand and his simulations are key to our eventual understanding of how these islands of stars formed and continue to shape themselves into the vast, varied structures we see today.
“This research has many potential implications for future observational astronomy, like the European Space Agency’s next corner stone mission, Gaia, which MSSL is also heavily involved in. As well as helping us understand the evolution of our own galaxy, it may have applications for regions of star formation.”
– Robert Grand
The results were presented at the Royal Astronomical Society’s National Astronomy Meeting in Wales on April 20. Read the press release on the Royal Astronomical Society’s website here.
Top image: M81, a spiral galaxy similar to our own Milky Way, is one of the brightest galaxies that can be seen from Earth. The spiral arms wind all the way down into the nucleus and are made up of young, bluish, hot stars formed in the past few million years, while the central bulge contains older, redder stars. Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
In celebration of the 21st anniversary of the Hubble Space Telescope’s deployment into space, astronomers pointed Hubble at Arp 273. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA
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Hubble has now turned 21, and unlike human young adults, we don’t have to worry about it staying up all night carousing at orbital drinking establishments. Instead the space telescope celebrates by doing what is has done best the past two decades, taking a marvelous image. This dramatic look at Arp 273 shows the very photogenic group of interacting galaxies that glow bright with intense star formation, perhaps triggered by a little carousing the two galaxies are doing with each other as they approach and interact.
Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. The image shows a tenuous tidal bridge of material between the two galaxies that are actually separated by tens of thousands of light-years from each other. But still, the gravitational pull between the two is causing distortions: visible in the larger of the spiral galaxies, known as UGC 1810, is a distorted disc. The swathe of blue stars across the top is the combined light from clusters of intensely bright and hot young stars.
These massive stars glow fiercely in ultraviolet light. A series of uncommon spiral patterns in the large galaxy are a telltale sign of interaction, say the Hubble astronomers. The large, outer arm appears partially as a ring, a feature that is seen when interacting galaxies actually pass through one another, so astronomers believe the smaller companion actually dived deeply, but off-center, through UGC 1810.
The smaller, nearly edge-on companion below is known as UGC 1813. It also shows distinct signs of intense star formation at its nucleus.
The larger galaxy has a mass that is about five times that of the smaller galaxy. In unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric structure in the main spiral. Also in such encounters, the starburst activity typically begins earlier in the minor galaxy than in the major galaxy. These effects could be due to the fact that the smaller galaxies have consumed less of the gas present in their nucleus, from which new stars are born.
The image was taken on December 17, 2010, with Hubble’s Wide Field Camera 3 (WFC3).
Galaxy ESO 510-G13. Credit: NASA/ESA and The Hubble Heritage Team STScI/AURA
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This is an older image from Hubble but I came across it today and wanted to share it. It shows an unusual edge-on galaxy, that has been twisted by a recent collision with a nearby galaxy, and is in the process of being swallowed up. This could be a spiral sister to our own Milky Way, as the dust and arms of normal spiral galaxies appear flat when viewed edge-on. And the twisting effect could be an example of what could happen to our galaxy in about 3 billion years when it begins to collide with the Andromeda galaxy.
As the gravitational forces distort the structures of the galaxies as their stars, gas, and dust merge together, it also sparks star formation. In the outer regions of ESO 510-G13, especially on the right-hand side of the image, the twisted disk contains not only dark dust, but also bright clouds of new, blue stars.
Eventually, in millions of years, all the matter will coalesce and the activity and disturbances will die out, and ESO 510-G13 will become a normal-looking single galaxy.
This galaxy was first observed by ESO’s ground based telescopes, and Hubble’s Wide Field Planetary Camera 2 (WFPC2) observed ESO 510-G13 in April 2001.
NASA Administrator Charles Bolden gets choked up during the 30th anniversary of the shuttle program.
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CAPE CANAVERAL – With the shuttle program’s end less than three months away, NASA took time to honor the program that has been the focal point of the agency’s manned space flight efforts for the past thirty years. At 1 p.m., NASA’s Administrator, Charles Bolden, along with Kennedy Space Center Director Robert Cabana, astronaut Janet Kavandi, shuttle Endeavour’s Vehicle Manager Mike Parrish and STS-1 Pilot Robert Crippen spoke to NASA employees and members of the media regarding the programs long history and its many achievements.
However, the most important announcement of the day was where the remaining shuttles will go when the program draws to a close. It was announced that the space shuttle Enterprise, a test article of the shuttle design, will move from its current home at the Smithsonian’s National Air and Space Museum Steven F. Udvar-Hazy Center in Virginia to the Intrepid Sea, Air & Space Museum in New York. The Udvar-Hazy Center will be home for Discovery, which finished its last mission in March. Endeavour, which is being readied for its final flight at the end of this month, will go to the California Science Center in Los Angeles. Atlantis, which is currently scheduled to fly the last shuttle mission in June, will go to the Kennedy Space Center Visitor Complex in Florida.
From left-to-right: Former astronaut and KSC Director Robert Crippen, former astronaut and current NASA Administrator Charles Bolden, astronaut Janet Kavandi, former astronaut and current KSC Director Bob Cabana and shuttle Endeavour's Vehicle Manager Mike Parrish. Behind them is shuttle Atlantis, which will remain at Kennedy Space Center in Florida. Photo Credit: Jason Rhian
Although Bolden and Cabana are former astronauts, they were joined by one of the two men that flew the very first shuttle mission, STS-1 – Robert Crippen. This mission is viewed as one of the most risky test flights in history. If something had gone wrong during the first mission’s launch, Crippen and Commander John Young would have had to eject from Columbia – through the vehicle’s fiery plume. However, everything worked according to plan and Columbia landed at Edwards Air Force Base in California two days later.
The weight of the day’s events had an obvious impact on Bolden and Crippen, both of whom were visibly emotional during the presentation. Crippen’s comments detailed the feelings of many in that this is a bitter-sweet anniversary. Those in attendance supported the four-time shuttle veteran with loud applause when it was announced that Atlantis would remain at Kennedy Space Center.
Former NASA astronaut and current Kennedy Space Center Director Robert Cabana gestures toward shuttle Atlantis which will remain in Florida at the Kennedy Space Center Visitor Complex. Photo Credit: Jason Rhian
“Stay focused, “said Bolden during his comments, referring to the gap in manned space flight that is about to take place. “It’s been a rough day.”
There was also a guest appearance from the current members of the International Space Station who called in from on orbit. They apologized for not being able to attend – before they acknowledged it was thanks to the hard work of those present that they couldn’t be there. Astronauts Cady Coleman, Ron Garan were joined by ESA astronaut Paolo Nespoli as well as cosmonauts Dmitry Kondratyev, Andrey Borisenko and Alexander Samokutyaev. The station’s crew spoke about how the shuttle program made this international effort possible.
The crew of the International Space Station conduct a long-distance phone call to attendees at the 30th Anniversary event of the shuttle program. Photo Credit: Jason Rhian
On April 12, 1981, the space shuttle Columbia roared into orbit on the first mission of the shuttle program. The first crew only had two astronauts on board, Apollo veteran John Young and rookie astronaut Robert Crippen. The first flight of the shuttle program took place 20 years to the day that the first human rode fire into orbit – Yuri Gagarin.
There are currently only two shuttle flights remaining, Endeavour is slated to conduct its 25th and final mission, STS-134, at the end of this month and Atlantis will launch the final mission on June 28. Once this mission is over, NASA will have to rely on Russia for access to the International Space Station until small, commercial firms; those supported under President Obama’s new plans for NASA can produce a launch system to fill the void.
“I would have been happy to get any of the orbiters here at KSC,” said Robert Crippen when interviewed. “Getting Atlantis makes this a very good day.”
The space shuttle Atlantis was on display, with commemorative banners from each of the orbiters. Atlantis will reside at Kennedy Space Center after her final flight this June. Photo Credit: Jason Rhian
mages from Swift's Ultraviolet/Optical (white, purple) and X-ray telescopes (yellow and red) were combined in this view of GRB 110328A. The blast was detected only in X-rays, which were collected over a 3.4-hour period on March 28. Credit: NASA/Swift/Stefan Immler
NASA’s Swift, Hubble Space Telescope and Chandra X-ray Observatory have teamed up to study one of the most puzzling cosmic blasts yet observed. More than a week later, high-energy radiation continues to brighten and fade from its location.
Astronomers say they have never seen anything this bright, long-lasting and variable before. Usually, gamma-ray bursts mark the destruction of a massive star, but flaring emission from these events never lasts more than a few hours.
Although research is ongoing, astronomers say that the unusual blast likely arose when a star wandered too close to its galaxy’s central black hole. Intense tidal forces tore the star apart, and the infalling gas continues to stream toward the hole. According to this model, the spinning black hole formed an outflowing jet along its rotational axis. A powerful blast of X- and gamma rays is seen if this jet is pointed in our direction.
On March 28, Swift’s Burst Alert Telescope discovered the source in the constellation Draco when it erupted with the first in a series of powerful X-ray blasts. The satellite determined a position for the explosion, now cataloged as gamma-ray burst (GRB) 110328A, and informed astronomers worldwide.
This is a visible-light image of GRB 110328A's host galaxy (arrow) taken on April 4 by the Hubble Space Telescope's Wide Field Camera 3. The galaxy is 3.8 billion light-years away. Credit: NASA/ESA/A. Fruchter (STScI)
As dozens of telescopes turned to study the spot, astronomers quickly noticed that a small, distant galaxy appeared very near the Swift position. A deep image taken by Hubble on April 4 pinpoints the source of the explosion at the center of this galaxy, which lies 3.8 billion light-years away.
That same day, astronomers used NASA’s Chandra X-ray Observatory to make a four-hour-long exposure of the puzzling source. The image, which locates the object 10 times more precisely than Swift can, shows that it lies at the center of the galaxy Hubble imaged.
“We know of objects in our own galaxy that can produce repeated bursts, but they are thousands to millions of times less powerful than the bursts we are seeing now. This is truly extraordinary,” said Andrew Fruchter at the Space Telescope Science Institute in Baltimore.
NASA's Chandra X-ray Observatory completed this four-hour exposure of GRB 110328A on April 4. The center of the X-ray source corresponds to the very center of the host galaxy imaged by Hubble (red cross). Credit: NASA/CXC/ Warwick/A. Levan
“We have been eagerly awaiting the Hubble observation,” said Neil Gehrels, the lead scientist for Swift at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The fact that the explosion occurred in the center of a galaxy tells us it is most likely associated with a massive black hole. This solves a key question about the mysterious event.”
Most galaxies, including our own, contain central black holes with millions of times the sun’s mass; those in the largest galaxies can be a thousand times larger. The disrupted star probably succumbed to a black hole less massive than the Milky Way’s, which has a mass four million times that of our sun
Astronomers previously have detected stars disrupted by supermassive black holes, but none have shown the X-ray brightness and variability seen in GRB 110328A. The source has repeatedly flared. Since April 3, for example, it has brightened by more than five times.
Scientists think that the X-rays may be coming from matter moving near the speed of light in a particle jet that forms as the star’s gas falls toward the black hole.
“The best explanation at the moment is that we happen to be looking down the barrel of this jet,” said Andrew Levan at the University of Warwick in the United Kingdom, who led the Chandra observations. “When we look straight down these jets, a brightness boost lets us view details we might otherwise miss.”
This brightness increase, which is called relativistic beaming, occurs when matter moving close to the speed of light is viewed nearly head on.
Astronomers plan additional Hubble observations to see if the galaxy’s core changes brightness.
A1689-zD1, one of the brightest and most distant galaxies, is 12.8 billion light years away - an extremely far distance in our expanding universe. Image credit: NASA/ESA/JPL-Caltech/STScI
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Welcome back to the third, and last, installment of Cosmology 101. So far, we’ve covered the history of the universe up to the present moment. But what happens next? How will our universe end? And how can we be so sure that this is how the story unfolded?
Robert Frost once wrote, “Some say the world will end in fire; some say in ice.” Likewise, some scientists have postulated that the universe could die either a dramatic, cataclysmic death – either a “Big Rip” or a “Big Crunch” – or a slower, more gradual “Big Freeze.” The ultimate fate of our cosmos has a lot to do with its shape. If the universe were open, like a saddle, and the energy density of dark energy increased without bound, the expansion rate of the cosmos would eventually become so great that even atoms would be torn apart – a Big Rip. Conversely, if the universe were closed, like a sphere, and gravity’s strength trumped the influence of dark energy, the outward expansion of the cosmos would eventually come to a halt and reverse, collapsing on itself in a Big Crunch.
Despite the poetic beauty of fire, however, current observations favor an icy end to our universe – a Big Freeze. Scientists believe that we live in a spatially flat universe whose expansion is accelerating due to the presence of dark energy; however, the total energy density of the cosmos is most likely less than or equal to the so-called “critical density,” so there will be no Big Rip. Instead, the contents of the universe will eventually drift prohibitively far away from each other and heat and energy exchange will cease. The cosmos will have reached a state of maximum entropy, and no life will be able to survive. Depressing and a bit anti-climactic? Perhaps. But it probably won’t be perceptible until the universe is at least twice its current age.
At this point you might be screaming, “How do we know all this? Isn’t it all just rampant speculation?” Well, first of all, we know without a doubt that the universe is expanding. Astronomical observations consistently demonstrate that light from distant stars is always redshifted relative to us; that is, its wavelength has been stretched due to the expansion of the cosmos. This leads to two possibilities when you wind back the clock: either the expanding universe has always existed and is infinite in age, or it began expanding from a smaller version of itself at a specific time in the past and thus has a fixed age. For a long time, proponents of the Steady State Theory endorsed the former explanation. It wasn’t until Arno Penzias and Robert Wilson discovered the cosmic microwave background in 1965 that the big bang theory became the most accepted explanation for the origin of the universe.
Why? Something as large as our cosmos takes quite a while to cool completely. If the universe did, in fact, began with the kind of blistering energies that the big bang theory predicts, astronomers should still see some leftover heat today. And they do: a uniform 3K glow evenly dispersed at every point in the sky. Not only that – but WMAP and other satellites have observed tiny inhomogeneities in the CMB that precisely match the initial spectrum of quantum fluctuations predicted by the big bang theory.
What else? Take a look at the relative abundances of light elements in the universe. Remember that during the first few minutes of the cosmos’ young life, the ambient temperature was high enough for nuclear fusion to occur. The laws of thermodynamics and the relative density of baryons (i.e. protons and neutrons) together determine exactly how much deuterium (heavy hydrogen), helium and lithium could be formed at this time. As it turns out, there is far more helium (25%!) in our current universe than could be created by nucleosynthesis in the center of stars. Meanwhile, a hot early universe – like the one postulated by the big bang theory – gives rise to the exact proportions of light elements that scientists observe in the universe today.
But wait, there’s more. The distribution of large-scale structure in the universe can be mapped extremely well based solely on observed anisotropies in the CMB. Moreover, today’s large-scale structure looks very different from that at high redshift, implying a dynamic and evolving universe. Additionally, the age of the oldest stars appears to be consistent with the age of the cosmos given by the big bang theory. Like any theory, it has its weaknesses – for instance, the horizon problem or the flatness problem or the problems of dark energy and dark matter; but overall, astronomical observations match the predictions of the big bang theory far more closely than any rival idea. Until that changes, it seems as though the big bang theory is here to stay.
