Quasars

  • "Quasi-stellar" radio sources
  • Very high redshifts – v~.3c
  • Must be very far away
    • 100’s to 1000’s Mpc
    • Must be extremely luminous
  • Powered by supermassive black holes

Light left this quasar when the earth was being formed

Explanation: The quasar known as PKS 1127-145 lies ten billion light-years from our fair planet. A Hubble Space Telescope view in the left panel shows this quasar along with other galaxies as they appear in optical light. The quasar itself is the brightest object in the lower right corner. In the right panel is a Chandra Observatory x-ray picture, exactly corresponding to the Hubble field. While the more ordinary galaxies are not seen in the Chandra image, a striking jet, nearly a million light-years long, emerges from the quasar to dominate the x-ray view. Bright in both optical and x-ray light, the quasar is thought to harbor a supermassive black hole which powers the jet and makes PKS 1127-145 visible across the spectrum -- a beacon from the distant cosmos.

 

5 bright white points are all images of the same quasar, mass is probably equal to hundreds of galaxies combined

APOD GRB 090423: The Farthest Explosion Yet Measured Credit: Gemini Observatory / NSF / AURA, D. Fox & A. Cucchiara (Penn State U.), and E. Berger (Harvard Univ.) Explanation: An explosion so powerful it was seen clear across the visible universe was recorded in gamma-radiation last week by NASA's orbiting Swift Observatory. Farther than any known galaxy, quasar, or optical supernova, the gamma-ray burst recorded last week was clocked at redshift 8.2, making it the farthest explosion of any type yet detected. Occurring only 630 million years after the Big Bang, GRB 090423 detonated so early that astronomers had no direct evidence that anything explodable even existed back then. The faint infrared afterglow of GRB 090423 was recovered by large ground telescopes within minutes of being discovered. The afterglow is circled in the above picture taken by the large Gemini North Telescope in Hawaii, USA. An exciting possibility is that this gamma-ray burst occurred in one of the very first generation of stars and announced the birth of an early black hole. Surely, GRB 090423 provides unique data from a relatively unexplored epoch in our universe and a distant beacon from which the intervening universe can be studied.

 

Active supermasive black holes

  • Extremely luminous
  • Light spectrum is nonstellar
  • Energy output is often variable
  • Powered by accretion disks
  • Typically have jets
    • Flow along magnetic field lines
    • Exhibit synchotron radiation
      • Highly relativistic electrons in plasma

Pearson image. Synchotron radiation intensity decreases with frequency because for length contraction of relativistic electrons. In a synchotron, the electrons’ motion radially toward the observer sees a shortened distance, hence a longer wavelength. As the angle increases, the wave encounters less length contraction, so higher frequency, but lower intensity because the propagation is peripheral. In an AGN, the signal is not as clean, but still has a dominant spread of radiation due to the spiraling particles, and a decrease in intensity for higher frequencies.

 

Diagram of an active galactic nucleus

Artist conception of an active galactic nucleus

Molecular Torus Surrounds Black Hole Explanation: Why do some black hole surroundings appear brighter than others? In the centers of active galaxies, supermassive black holes at least thousands of times the mass of our Sun dominate. Many, called Seyfert Type I, are very bright in visible light. Others, called Seyfert Type II, are rather dim. The difference might be caused by some black holes accreting much more matter than others. Alternatively, the black holes in the center of Seyfert Type II galaxies might be obscured by a surrounding torus. To help choose between these competing hypotheses, the nearby Seyfert II galaxy NGC 4388 has been observed in X-ray light recently by many recent Earth-orbiting X-ray observatories, including CGRO, SIGMA, BeppoSAX, INTEGRAL, Chandra, and XMM-Newton. Recent data from INTEGRAL and XMM-Newton have found that the X-ray flux in some X-ray colors varies rapidly, while flux in other X-ray colors is quite steady. The constant flux and apparent absorption of very specific X-ray colors by cool iron together give evidence that the central black hole in NGC 4388 is seen through a thick torus composed of molecular gas and dust.

 

http://solar-center.stanford.edu/art/black-hole.html

The colorful "zigzag" on the right is not the work of a flamboyant artist, but the signature of a supermassive black hole in the center of galaxy M84, discovered by Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS).

The image on the left, taken with Hubble's Wide Field Planetary and Camera 2 shows the core of the galaxy where the suspected black hole dwells. Astronomers mapped the motions of gas in the grip of the black hole's powerful gravitational pull by aligning the STIS's spectroscopic slit across the nucleus in a single exposure.

The STIS data on the right show the rotational motion of stars and gas along the slit. The change in wavelength records whether an object is moving toward or away from the observer. The larger the excursion from the centerline -- as seen as a green and yellow picture element (pixels) along the center strip, the greater the rotational velocity. If no black hole were present, the line would be nearly vertical across the scan.

Instead, STIS's detector found the S-shape at the center of this scan, indicating a rapidly swirling disk of trapped material encircling the black hole. Along the S-shape from top to bottom, velocities skyrocket as seen in the rapid, dramatic swing to the left (blueshifted or approaching gas), then the region in the center simultaneously records the enormous speeds of the gas both approaching and receding for orbits in the immediate vicinity of the black hole, and then an equivalent swing from the right, back to the center line.

STIS measures a velocity of 880,000 miles per hour (400 kilometers per second) within 26 light-years of the galaxy's center, where the black hole dwells. This motion allowed astronomers to calculate that the black hole contains at least 300 million solar masses. (Just as the mass of our Sun can be calculated from the orbital radii and speeds of the planets.)

This observation demonstrates a direct connection between a supermassive black hole and activity (such as radio emission) in the nucleus of an active galaxy. It also shows that STIS is ideally suited for efficiently conducting a survey of galaxies to determine the distribution of the black holes and their masses.

Each point on STIS's solid-state CCD (Charge Coupled Device) detector samples a square patch at the galaxy that is 12 light-years on a side. The detection of black holes at the centers of galaxies is about 40 times faster than the earlier Faint Object Spectrograph. STIS was configured to record five spectral features in red light from glowing hydrogen atoms as well as nitrogen and sulfur ions in orbit around the center of M84. At each sampled patch the velocity of the entrapped gas was measured. Because the patches are contiguous, the astronomers could map the change of velocity in detail.

Hubble deep field