Most Distant Quasar Discovered

Late last month, astronomers announced the discovery of the most distant known quasar, designated ULAS J1120+0641.  About 28.85 billion light years away, this quasar challenges many of our ideas about the early universe.

A quasar (or quasi-stellar object) is the central region of a massive galaxy, from 10 to 10,000 times as big across as that galaxy’s central black hole.  Material forming an accretion disk around these supermassive black holes emits the radiation we see as the quasar. A quasar is generally so luminous as to make the rest of its galaxy invisible by comparison.  For example, this particular quasar emits over six trillion times as much light as our sun.

This artist’s impression shows how ULAS J1120+0641, a very distant quasar powered by a black hole
with a mass two billion times that of the sun, may have looked. This quasar is the most distant yet found
and is seen as it was just 770 million years after the Big Bang. This object is by far the brightest object
yet discovered in the early Universe. Photo Credit: ESO/M. Kornmesser

Daniel Mortlock of the Imperial College London and his colleagues used the United Kingdom Infrared Telescope on Mauna Kea, Hawaii, to search for objects that did not show up in visual light surveys of the same area of the sky.  This allowed them to isolate objects of very high redshift.  In time their search revealed the quasar ULAS J1120+0641.

The numbers in the quasar’s designation are its celestial coordinates: right ascension 11 hours 20 minutes and declination +6 degrees and 41 minutes.  This position is in the constellation Leo, the Lion.  Before publishing their results, the astronomers used spectra taken at the Gemini North Telescope (in Hawaii) and the Very Large Telescope (in Chile) to establish a specific redshift of 7.085, the highest redshift known for a quasar as of June 2011.

Redshift occurs because when an object is receding from us, we see the light it emits at a longer wavelength than it would otherwise have.  In the visible spectrum, red and orange light has the longest wavelengths and blue and violet light the shortest.  Thus the lengthening of wavelength in light from an object moving away from us is a redshift.

The expansion of the universe that began with the Big Bang involves the creation of new space in between distant galaxies rather than their motion through space.  As a result, more distant galaxies recede from us faster than those nearby.  Larger redshifts, then, indicate greater distances.  For example, most of the light this quasar emitted was actually ultraviolet light, with a shorter wavelength than we can see.  However, we see its light redshifted into the infrared, at wavelengths longer than we can see.

We determine redshift by taking a spectrum of light from a celestial object and looking for absorption lines.  These are dark lines in an other wise continuous spectrum, indicating wavelengths absorbed by gases.  Since we know which wavelengths gases such as hydrogen or oxygen readily absorb, contrasting the observed absorption lines with these normally absorbed wavelengths reveals the redshift.  In particular, we can relate the redshift z to the wavelengths of absorption lines in this equation:

1+z = λoe

where λe is the wavelength normally observed by a particular gas, and λo is the wavelength of the observed absorption line.  A negative z indicates a blueshift, in which an object is approaching the observer.

A redshift of 7.085 corresponds to a distance of 28.85 billion light years.  (Such distances are indeed possible, even though the universe is 13.7 billion years old, if we consider that the universe has greatly expanded in those 13.7 billion years).  It also means that when we look at this quasar, we are looking about 13 billion years in the past, to a time about 770 million years after the Big Bang.

Electromagnetic Spectrum
Photo Credit: Materialscientist

Interestingly, this is so early in the history of the universe that it may precede the era of reionization.  About 380,000 years after the Big Bang, the universe had cooled enough to allow neutral hydrogen atoms to form.  At a later time, less than one billion years after the big bang, newly formed galaxies began to emit radiation energetic enough to reionize hydrogen atoms (i.e. liberate the electron from the proton).  Monckton concluded that the spectra of ULAS J1120+0641 indicate up to 10-50% neutral hydrogen, while spectra of most quasars indicate less than one percent.  This is our first direct glimpse of a period so early in the history of the galaxy.

A surprising result is that the central black hole of the galaxy containing ULAS J1120+0641 has a mass about 2 billion times our sun’s mass.  Current models do not predict that a black hole that massive could form so soon after the Big Bang.

Once again, the universe proves more wondrous than we can imagine.

Is anyone else out there? [Life in the Universe]

Are we alone in the universe? Is there intelligent life out there?

If you escape from the city lights and stare up at the night sky, you will see hundreds of stars. With a telescope you can see thousands, and with the help of the Hubble and computers we can see millions of stars.

Our sun has eight (nine if you’re sentimental like me) planets circling it. Not every star is going to have planets, but others will have multiple. How many million of unexplored planets are there out in the universe? Also remember that most of the stars we can see are located within our own galaxy, and that there are countless other galaxies with countless other stars and planets.

With so many billions of planets and moons, I personally believe there is at least some form of life out there in the universe. And although these may just be simple life forms, there is also a good chance that there is intelligent life somewhere in the universe.

For those of you who stare up at the night sky and wonder about the universe, we have a new planetarium show just for you, opening today.

Life in the Universe first explores our own solar system and discusses the possibility and likelihood of whether there could be simple life hidden somewhere beneath the surface of a planet or moon. Second, it delves into the galaxy and universe around us, discussing whether or not we might be alone in the universe, and why we haven’t been able to find anyone else so far.

For those of you who are interested in whether or not little green men might soon invade, or just want to learn more about the solar system, the galaxy and the universe that we live in, come on down to the Burke Baker Planetarium and check out Life in the Universe.

This month, see a ‘Hairy Star!’

An unexpected visitor graces our skies this month.  Comet Lulin is now visible through binoculars in late evening and morning skies.  It makes its closest approach to Earth on February 24, when it may even be dimly visible to the naked eye!

Comet Hale-Bopp
Creative Commons License photo credit: tlindenbaum

Comets are made of ice and dust and are often called ‘dirty snowballs.’ They are believed to be left over from the formation of the solar system.  As comets approach the sun, ice changes into gas and the dust embedded within the ice is released.  A cloud of particles expands out to form a coma around the comet’s solid nucleus. This coma may be a hundred thousand miles across. Radiation pressure of sunlight and the powerful solar wind sweep gases and dust off of the comet, forming tails pointing away from the Sun. The coma and tails of a comet reminded the ancient Greeks of hair; the Greek word ‘kometes’ means ‘hairy.’   

Astronomers traditionally name comets after their discoverers.  On July 11, 2007, Lin Chen-Sheng of Lulin Observatory in Nantou, Taiwan took some photographs of the sky.  The photos were part of the Lulin Sky Survey, in which astronomers search the sky for Near-Earth Objects which might pose a risk of colliding with Earth.  One of his students, Ye Quanzhi, spotted what he thought was an asteroid in three of the pictures.  Closer observation, however, revealed the coma of a comet.  Officially designated C/2007 N3, the comet was named Lulin after the observatory where it was discovered. 

Here are some interesting facts about Comet Lulin’s orbit:

The eccentricityof an orbit describes its shape.  Bound orbits are ellipses with eccentricities between 0 and 1; 0 is a perfect circle while 1 is a parabola.  Lulin has an eccentricity of 0.9999948, almost 1.  This indicates an orbit so oblong that Lulin won’t return to the inner solar system for about 50 million years.  Some sources indicate an eccentricity slightly greater than 1.  In that case, Lulin will never again approach the Sun.

Lulin was closest to the Sun (at perihelion) on January 10.  But it approached the Sun from the far side (from our perspective).  Thus, as Lulin recedes from the Sun, it approaches Earth, with closest approach on February 24.  Not to worry, though–even at its closest, Lulin will be about 150 times as far away as the Moon.

Many comets’ orbits are highly inclined to ours.  (An inclination of 0 degrees would describe an orbit in the same plane as Earth’s orbit.)  Comet Lulin has an inclination of 178.37 degrees.   This inclination of almost 180 degrees puts Lulin back in the plane of the solar system, orbiting backwards compared to the planets’ orbits. 

Since Lulin orbits almost in Earth’s orbital plane, we see not only a tail but an ‘anti-tail.’  This is dust and debris left behind as the comet moves on its path.  Lulin is now moving away from the Sun, so the dust it leaves behind seems to point towards the Sun. The true tail of a comet always points away from the Sun (and therefore, the tail leads the comet as it moves away from the Sun). 

The Hale-Bopp Comet
Creative Commons License photo credit: Wolfiewolf

Because Lulin is roughly in the plane of the solar system, traveling backwards, it appears against the same zodiac band where we find the Sun, Moon, and planets in our sky.  As I type this, Lulin is among the stars of Virgo, the Virgin, moving towards Leo, the Lion. 

As we pass more or less between the Sun and Lulin next week, we’ll see it in Leo, first near Saturn and then near the bright star Regulus.  Lulin will be rising in the east at about dusk, highest in the sky about midnight, and setting in the west just before dawn.  Since Lulin and Earth are going in opposite directions, we see Lulin move quite noticeably night to night. 

This page has some finder charts for Lulin.  Some observers have reported seeing Lulin naked-eye, at the threshold of visibility.  You must get far from city lights, therefore, to see it without binoculars or a telescope.  Remember to scan the sky for a diffuse object about half as big across as the full Moon (and much dimmer than that), not a point of light.  Those who saw the spectacular comets Hyakutake and Hale-Bopp in the ’90s should keep in mind that Lulin will be barely (if at all) be visible to the unaided eye and will not come close to their displays.  If you find Lulin, see if you can follow it as it gets dimmer but higher in the evening sky in March. 

Once it fades away, we’ll never see it again. 

The Great Cosmic Year

Our Milky Way Galaxy..
Creative Commons License photo credit: Sir Mervs

One of the biggest challenges in teaching astronomy to kids – or even to the general public – is that astronomy involves numbers so big as to be virtually meaningless. Consider the age of the universe, for example. Our best data indicate that the Big Bang, where space and time began, occurred about 13.7 billion years ago. As very few of us have seen 13.7 billion of anything before, how can we appreciate how long a time that is?

One way is to use a scale-model. Just as we use globes because the real Earth is too big to look at, we can ‘shrink’ the 13.7 billion year history of the universe into one year. Imagine a Great Cosmic Year, in which the Big Bang occurs at 12:00:00 am on January 1 and the present moment is 11:59:59.9999999 pm on December 31. On this time scale, each day represents (13.7 billion/365) years, or about 37.5 million years. Our best estimates for when the events listed below occurred are approximate; the dates listed may need to be adjusted slightly in the future.

Still, locating the events in the history of the universe, the Sun, and the Earth on this calendar can give us a better sense of how much time is involved.

January 1, midnight The Big Bang occurs.

January 13 The oldest known star in our galaxy (designated HE 1523-0901) forms.

‘HE’ here refers to the Hamburg/ESO (European Southern Observatory) survey, in which the star is catalogued. Being about 100 times too dim to be seen with the unaided eye, the star has no common name. It is in the constellation Libra.

Planet Earth (III)
Creative Commons License photo credit: Aaron Escobar

January 4-27 Re-ionization occurs.

We take for granted that the universe is transparent; that we can look through space and see galaxies, stars, and other planets. However, once hydrogen atoms formed in the early universe, this would have been impossible, as hydrogen atoms readily absorb photons (light particles). After the first billion years (corresponding to January 27 in the Great Cosmic Year), the hydrogen had been re-ionized. This happens when the electron in the hydrogen atom is too energetic too remain in orbit around the single proton which makes up the hydrogen nucleus. Newly formed stars and galaxies provided much of this energy.

April 14 First Sun-like stars (population I) appear.

Hydrogen and helium are so abundant in the universe that astronomers lump all other elements into a catch-all category called ‘metals.’ Astronomers divide stars into three categories based on their ‘metallicity,’ or how much stuff other than H or He they contain. This is important because those ‘metals’ ultimately make up solid things such as planet Earth, or you or me. Our Sun is only about 2% ‘metal.’

Stars of comparable metallicity are the youngest and are placed in population I. Some older stars in the distant halo of our galaxy are much less ‘metallic’ than our Sun, in some cases by a factor of 1,000 or 10,000; these are population II stars. Since all elements heavier than helium are formed in stars, astronomers speculate that the very first stars had virtually no metals, but such ‘population III’ stars have yet to be discovered.

It took about four billion years to make the first population I stars, bringing us to April 14 in our Great Cosmic Year.

Andromeda, again.
Creative Commons License photo credit: makelessnoise

May 23 The Milky Way’s galactic thin disc forms. This part of our galaxy includes our Sun.

August 31 Our solar system forms from a spinning cloud of dust.

The first population I stars to formed back on ‘April 14’ did not include our Sun. Astronomers recently discovered decay products of 60Fe, an isotope of iron that results from supernovae (exploding stars), in some meteorites. This suggests that a nearby supernova ejected this material into the dust cloud that became our solar system, making our sun at least a second generation population I star.

September 2 Earth begins to form.

Bad Moon Rising
Creative Commons License photo credit: makelessnoise

September 3 The Moon forms when a Mars-sized object called ‘Theia’ strikes Earth.

September 21 Earth begins to solidify.

This corresponds to the end of the Late Heavy Bombardment, a period of frequent impacts on all bodies in the inner solar system. Up to this point, consistent bombardment kept the Earth molten, with magma seas. With the end of the bombardment, Earth began to cool, solid rocks appeared, and Earth’s geologic history began.

September 29 Life begins on Earth.

October 12 The first continent (called Ur) appears on Earth.

November 2 Oxygen (O2) builds up in Earth’s atmosphere.

November 14 Eukaryotes (with distinct nuclei in the cell) exist on Earth.

November 27 Multicellular organisms exist.

December 5 The supercontinent Rodinia forms.

December 17 Cambrian explosion: earliest forms of most types (phyla) of animals appear.

December 20 First life on land

Of course, the real dinosaurs were bigger,
and not made of paper.
Creative Commons License
photo credit: kekremsi

December 25-29 Age of the dinosaurs

December 30 (morning) Chicxulub meteor impact helps cause extinction of about 3/4 of all life, including the dinosaurs.

The following events all occur on December 31:

9:17 am Drake passage completes the isolation of Antarctica; the continent freezes over.

7:30 pm Human ancestors diverge from chimpanzees.

9:57 pm Lucy lives in east Africa.

11:52 pm Homo sapiens sapiens exists.

11:59:14 pm Last Glacial Maximum (most recent Ice Age)

11:59:45pm Uruk, in Sumer, is one of the first cities on Earth.

Our existence as a species, compared to the whole universe, is about eight minutes out of a year. All of human civilization amounts to about 15 seconds. Once, I presented this calendar and was told that the smallness of our existence was an attack on religious faith. Perhaps, however, this need not be so. After all, an important virtue in most religious traditions is humility. This is not the denial of our talents and value, but the realization that we, with our goals, hopes, and dreams, are but one element of a much larger whole. As you reflect back on 2008 this holiday season, I invite you to reflect on the Great Cosmic Year. I find that the resulting wonderment and awe deepens my appreciation of the universe, and reminds me why I studied science in the first place.