First black hole image: a photo using radio waves

While I was writing the previous post about Einstein's remark that he couldn't "warm up" to Planck's idea of oscillators that have "fixed period and damping" being able to produce a thermal spectrum, the news came out--on that same day--that a photo had been made of a black hole. Mainly, the photo itself came out.  And it is stunning!  

It shows what's called the accretion disk around the black hole at the center of a super-giant elliptical galaxy called M87, 55 million light years away from our Milky Way galaxy.  The disk happens to be oriented so that it's visible from Earth, which means we aren't looking at it along its edge, but are instead looking at it from above or below.  This is just like viewing a doughnut from an angle where the hole is visible, not from the side. An accretion disk is made up of small particles of matter* that form into the doughnut-like shape as they orbit a massive astronomical object, which could be a star or the remnant of a star (neutron star, white dwarf, black hole). The particles emit radiation as a result of accelerating and also colliding as they fall inward while orbiting.

I haven't seen any discussions yet of whether the disk around the black hole in M87 would be viewable in the visible spectrum if we were a lot closer than 55 million light years away from it.  (The Milky Way is 100,000 light years in diameter, or 0.1 million light years, so M87 is 550 times as far away as the size of the Milky Way.  The Andromeda galaxy, the closest normal galaxy to us, is about 2.5 million light years away, or 25 times the size of the Milky Way.)

Since the M87 black hole is so massive, 6.5 billion times the mass of the sun, it accelerates particles in the accretion disk to high velocities resulting in radiation in the x-ray region of the electromagnetic spectrum,* in the range of 0.1 to 10 nanometers. Visible light has wavelengths in the range of 350-750 nanometers or 0.00035-0.00075 millimeters.

The "photograph" of the M87 black hole accretion disk was made using radio waves near the one-millimeter wavelength range. That was necessary because radio telescopes had to be used due to the extreme angular smallness of  M87 as viewed from Earth, said to be the same angular size as a grapefruit on the moon's surface as viewed from Earth, which is 40-microarcseconds.  For comparison, the resolution capability of the Hubble space telescope is only 50,000 microarcseconds.  (The smaller the number, the better the resolution.)

To achieve this kind of angular resolution the image was made using radio telescopes located at eight different places around the world.  The radio frequencies and their intensities were measured by the synchronized telescopes, then stored on many hard drives that were flown to two supercomputer processing centers.  To represent the resulting radio frequency data visually, the frequencies and intensities were proportionally transformed into reddish-orange light, 600-700 nanometers, as seen in the "photo".

A good description of accretion disks can be found here, along with an old Hubble Telescope photo of the "giant plasma jet" being emitted from M87.  A good article on obtaining the M87 black hole image is in Wired.  A description of the galaxy M87 can be found many places, including here.  The constellation Virgo in which M87 is found is visible early in the evening during this time of year. 


*Addendum:  See the Wikipedia article on M87, which says among other things that the black hole there is a strong emitter of gamma rays (even more energetic than x-rays), and that the accretion disk is made of ionized gas rather than larger particles, which makes sense since solid particles would be vaporized (turned into gas) as they heated up.  Also, regarding radio waves being represented as color photos, see this discussion on the Physics Stack Exchange.

Einstein not "warming up to" Planck in 1901

Here's an excerpt from a letter that 22 year-old Albert Einstein wrote on April 10, 1901 to his girlfriend or maybe by then  fiancée, Mileva Maric:

Planck assumes that a completely definite kind of resonator (fixed period and damping) causes the conversion of energy to radiation, an assumption I cannot really warm up to.

Einstein was making a play on words at the end of the sentence, since Planck's work involved the theory of "heat radiation," the radiation emitted by an object due solely to its temperature. See the full English translation of the letter, plus much more, at the Einstein Papers Project website.

(The reference in Einstein's letter to "Dude" should be to "Drude" instead, one of the great physicists of the early 20th century who committed suicide.  Boltzmann and Ehrenfest are the other two.)

For about 15 more years, Einstein continued to be dissatisfied with the general lack of a physical description of  "the mechanism of energy transfer" for the radiation absorption and emission of a charged harmonic oscillator ("resonator"). One of the relevant questions was, how can an oscillator emit or absorb light in discrete packets when it's oscillating continuously?

In fact, a physically meaningful description still doesn't exist for either the quantum harmonic oscillator or the quantum emission and absorption of light by atoms.  As a substitute explanation, we currently have only the highly developed perturbation theory of quantum mechanics, which works spectacularly but is nevertheless a mathematical invention, not a physical explanation.  This state of affairs is one that Einstein himself helped to set into motion in 1916-17, when he re-derived the Planck black-body radiation spectrum equation using what are now called the Einstein A and B coefficients, which are based on probability considerations.