Missing Black Holes Found

Astronomers have discovered hundreds of black holes hiding deep inside dusty galaxies billions of light-years away.

The massive and growing black holes, discovered by NASA's Spitzer and Chandra space telescopes, represent a large fraction of a long-sought missing population. Their discovery implies there were hundreds of millions of additional black holes growing in our young universe, more than doubling the total amount known at that distance.

The discovery reveals that active, supermassive black holes were everywhere in the early universe. The findings are also the first direct evidence that most, if not all, massive galaxies in the distant universe spent their youths building supermassive black holes at their cores.

A Primer on Black Holes and Quasars

A black hole is the common name for an object so dense that not even light can escape its gravity. It is detected by studying its effects on nearby objects and matter (infrared radiation, radio emissions, x-rays, etc.). A supermassive black hole is black hole that has a mass ranging from 100 thousand to over 100 billion solar masses (the mass of the sun). It is currently thought that most, if not all galaxies, including the Milky Way, contain supermassive black holes at their centers.

Those old enough to remember the 1970s may remember Motorola's Quasar brand of color televisions, as well as their slogan: "The quality goes in before the name goes on." Well, the brand name was a reference to the astronomical term.

Many pronounce the word as "QUAY-zar," though some insist that it should be pronounced "QUAH-zar." In any case, the word is a contraction of the phrase "quasi-stellar radio source." The first quasars were discovered in the 1950s using radio telescopes and many quasars were observed just as radio sources with no visible light source. It was not until the 1960s that the radio sources were first linked to visible objects. And the abbreviation "quasar" was first used in a 1964 scientific paper. Astronomers have found that only 10% of quasars actually have a strong radio emission. So the name "quasi-stellar object" or QSO is sometimes used for the majority class of objects that are "radio-quiet." Still, many often refer to all of these objects as quasars.

Today, scientists generally agree that a quasar is the compact doughnut of gas and dust that surrounds a very active supermassive black hole at the center of a young galaxy. As the gas and dust are devoured by the black hole, they heat up and shoot out X-rays. A quasar may release energy in levels equal to the output of hundreds of average galaxies combined. The X-rays can be detected as a general glow in space, but often the quasars themselves can't be seen directly because the surrounding doughnut blocks them from our view.

For decades, a large population of active black holes has been considered missing. Based on studies done about 30 years ago, astronomers knew that there must be more quasars in the universe, but they didn't know where or how to find them until now.

The Research Team

The research team was led by Emanuel Daddi, now of the Commissariat a l'Energie Atomique in France. Daddi began the project while working at the National Optical Astronomy Observatory (NOAO) in Tucson, Arizona before relocating to France last year. Another team member was Mark Dickinson, an astronomer with NOAO. Dickinson led the infrared segment of the investigation using NASA's Spitzer space telescope. Also on the team was David Alexander of Durham University, United Kingdom, and David Elbaz of the Commissariat a l'Energie Atomique. Daddi, Dickinson, Alexander, and Elbaz were co-author of two new papers that will appear in the November 10 issue of The Astrophysical Journal. The team’s results were consistent with those recently obtained by another team led by Fabrizio Fiore of the Osservatorio Astronomico di Roma, Italy. The results of the second team will appear in the Jan. 1, 2008, issue of Astrophysical Journal.

The Observations

The team initially set out to study 1,000 dusty and massive galaxies that were busy making stars. The galaxies were about the same mass as our own spiral Milky Way galaxy, but irregular in shape. Most important, the galaxies were also thought to not have quasars. The galaxies were (and still are) located 9 billion to 11 billion light years away, which meant the team was seeing the galaxies as they were 9 to 11 billion years ago. Since the universe is thought to be about 13.5 billion years old, that would mean the team was looking at a universe that was only 2.5 to 4.5 billion years old, so these 1,000 galaxies would have been in their teenage years - the boom time when the galaxies were growing the most.

When the team examined the galaxies with Spitzer, they noticed that about 200 of the galaxies gave off an unusual amount of infrared light. X-ray data from Chandra, and a technique called "stacking," revealed the 200 galaxies were, in fact, hiding plump quasars. The scientists now think that the quasars heat the dust in their surrounding doughnut clouds, releasing the excess infrared light.

Prior to the investigation, astronomers had only seen the rarest and most energetic black holes from the early universe. But the team’s discovery more than doubles that number of black holes. Some were comparing the experience to having a blindfold removed from their eyes. By projecting their results to the rest of the sky, the team now thinks it has found most of the population of hidden quasars in the early universes.

The Findings

The newfound quasars are helping answer fundamental questions about how massive galaxies evolve. For instance, astronomers have learned that most massive galaxies steadily build up their stars and black holes simultaneously until they get too big and their black holes suppress star formation. It is thought that supermassive black holes have to consume on average about 10 solar masses each year. But that the brightest known quasars have to consume about 1,000 solar masses of material per year. Since they cannot continue at this rate forever, scientists now think that after quasar accretes the surrounding doughnut gas and dust, it settles down to what we consider an ordinary galaxy. Eventually, when the supermassive black holes get “supermassive” enough, they actually prevent new stars from forming, and the galaxy slowly grows dark as the remaining stars die.

The observations also suggest that collisions between galaxies might not play as large a role in galaxy evolution as previously believed. Some had thought that the merging of galaxies was required to begin quasar activity, but they now see that quasars can be active in solitary galaxies.

The Survey

Daddi’s team made their observations as part of the Great Observatories Origins Deep Survey (GOODS), the most sensitive survey to date of the distant universe at multiple wavelengths. GOODS unites extremely deep observations from NASA's Great Observatories (the Spitzer Space Telescope, the Hubble Space Telescope, the Chandra X-ray Observatory), from ESA's XMM-Newton X-ray Observatory, and from the most powerful ground-based facilities, to survey the distant universe to the faintest detectable limits across the broadest range of wavelengths.

For more information on the team’s discovery, visit http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer; and http://chandra.harvard.edu/ and http://www.nasa.gov/mission_pages/chandra/main/index.html.

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THE SKY THIS WEEK

Oct 28 - Venus at greatest western elongation (46°)

Oct 30 - Mars is 3° south of the Moon

Oct 31 - Neptune is stationary. The body appears motionless in the sky due to the turning point between its direct and retrograde motion.

Nov 1 - Mercury is stationary. The body appears motionless in the sky due to the turning point between its direct and retrograde motion.

Nov 1, 5:18 P.M (EDT) - Last Quarter Moon

Nov 1 - Comet Arend perihelion (1.924 AU)

Nov 2 - Comet Arend closest approach to Earth (0.999 AU)

Nov 2 - Asteroid 1604 Tombaugh closest approach to Earth (1.881 AU)

Nov 3 - Peak of the Southern Taurid Meteor Shower. This is one of two showers visible in the fall and winter that originate from the constellation Taurus. Both of these showers appear to be caused by Periodic Comet Encke. The other shower is called the Northern Taurid shower The Southern Taurid meteors are visible from September 15 through December 15 with the peak on November 3. The average meteor rate ranges from 5 to 15 per hour. The coordinates for the radiant of the Southern Taurid shower is RA 03hrs 44min, +14°.

Meteors are best viewed from a dark-sky location. Observers in for the duration of the evening, or at least for several hours, should bring along a few things: a sleeping bag or blankets for warmth, a recliner or lawn chair, a hot beverage to help cut the chill, and binoculars to view the smoke trails of just-past meteors.

Nov 3 - Regulus is 0.03° north of the Moon, an occultation when viewed from some locations.

Nov 3 - Saturn is 1.8° north of the Moon

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THIS WEEK IN HISTORY

Oct 29, 1938 - Orson Welles' Broadcast of the "War of the Worlds"

Oct 30, 1981 - Venera 13 Launch (USSR Venus Lander/Flyby Mission)

Oct 30, 1999 - Discovery of the Los Angeles Meteorite (a Mars Meteorite)

Oct 31, 1936 - 1st Successful Rocket Engine Test in Pasadena, California (JPL's Beginnings)

November 2000 - Discovery of the NWA 480 Meteorite (a Mars Meteorite) in Morocco

Nov 2, 1885 - Harlow Shapley's Birthday

Nov 2, 1917 - 90th Anniversary, Mount Wilson 100-inch Telescope First Light

Nov 2, 2002 - 5th Anniversary, Stardust, Asteroid 5535 Annefrank Flyby

Nov 3, 1905 - August Kopff's Discovery of Asteroid 579 Sidonia

Nov 3, 1957 - 50th Anniversary, Sputnik 2 Launch (Laika Dog)

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MUSICAL DIVERSION

"The Ash Grove" is one of the few Welsh folk songs that has become known all over the world. The Welsh title is "Llwyn Onn" - "llywn" meaning "grove" and "onn" meaning "ash tree"

"According to Grove's Dictionary of Music and Musicians, a variation of the melody appeared as early as 1728. The song was called "Cease Your Funning" and it was part of the muscal "The Beggar Opera" by John Gay.

The more familiar tune is a very old harp melody that was first published (without words) in the 1802 collection entitled "The Bardic Museumsin" by Edward Jones (called "The King's Harpist"). About four years later the tune finally appeared with words in a collection that was appropriately entitled, "Welsh Melodies with Appropriate English Words."

Like many popular melodies, the tune of "The Ash Grove" has over the years been set to many texts. Some more suitable than others for singing in mixed company.

Among the more suitable texts are the Christian hymns, which include such titles as "Let All Things Now Living," "The Master Hath Come" and "On This Night Most Holy."

There are at least four Welsh texts for "The Ash Grove" and it is difficult to know which of these is truely the original, if any. The text below is one of the more popular of the four. It tells the sad story of a sailor's love for Gwen of Llwyn Onn. After her death, the sailor thinks only on Gwen and on other lost friends and loved ones. The Welsh text is in two stanzas and the English translation is in three, suggesting that either the Welsh language is more compact, or that some poetic license was used in the translation.

The Ash Grove

(Welsh)

Yn Nyffryn Llwyn Onn draw mi welais hardd feinwen
A minnau'n hamddena 'rol byw ar y don;
Gwyn ewyn y lli oedd ei gwisg, a disgleirwen
A'r glasfor oedd llygaid Gwen harddaf Llwyn Onn.
A ninnau'n rhodiana drwy'r lonydd i'r banna,
Sibrydem i'n gilydd gyfrinach byd serch;
A phan ddaeth hi'n adeg ffarwelio a'r wiwdeg,
Roedd tannau fy nghalon yng ngofal y ferch.

Cyn dychwel i borthladd wynebwn y tonnau,
Ond hyfryd yw'r hafan 'rol dicter y don;
Bydd melys anghofio her greulon y creigiau--
Un felly o'wn innau 'rol cyrraedd Llwyn Onn.
A thawel mordwyo wnaf mwyach a Gwenno
Yn llong fach ein bwthyn a hi wrth y llyw;
A hon fydd yr hafan ddiogel a chryno
I'r morwr a'i Wenno tra byddwn ni byw.

(English translation by John Oxenford)

The ash grove, how graceful, how plainly 'tis speaking,
The wind [harp] through it playing has language for me.
Whenever the light through its branches is breaking
A host of kind faces is gazing on me.
The friends of my childhood again are before me,
Each step wakes a memory as freely I roam.
With soft whispers laden its leaves rustle o'er me,
The ash grove, the ash grove again [alone] is my home.

My laughter is over, my step loses lightness,
Old countryside measures steal soft on my ear;
I only remember the past and its brightness,
The dear ones I mourn [long] for again gather here.
From out of the shadows their loving looks greet me
And wistfully searching the leafy green dome,
I find other faces fond bending to greet me,
The ash grove, the ash grove alone is my home.

My lips smile no more, my heart loses its lightness
No dream of my future my spirit can cheer;
I only can brood on the past and its brightness,
The dead I have mourned are again living here.
From ev'ry dark nook they press forward to meet me;
I lift up my eyes to the broad leafy dome,
And others are there looking downward to greet me;
The ash grove, the ash grove alone is my home.


To review some the history, the text, or to listen to the melody, check out this page from the "Songs of Wales" section of "Contemplations from the Marianas Trench - Music and Deep Thoughts" - http://www.contemplator.com/wales/ashgrv.html

To see a GIF image file of the score of the song, or to download an ABC file of the score, visit this page of "The Session" - http://www.thesession.org/tunes/display/997

To see and hear more on the hymn, "The Master Hath Come," visit this page of "The Cyber Hymnal" - http://www.cyberhymnal.org/htm/m/a/masthath.htm

For further detailed information about this tune and many different sets of lyrics in English and Welsh go to www.gurman.org/ashgrove

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