Enormous Ring of Dust Could be a Stellar Pregnancy
The Atacama Large Millimeter/Submillimeter Array, or ALMA, is nearing completion after over 30 years of planning and collaborating among astronomers and engineers from several nations. The completed array will consist of 66 antennas and two supercomputers, called correlators, at the backend to collect the signals and make the array function as one large telescope.
On March 12th and 13th, 2013, over a hundred journalists descended upon the array along with politicians, scientists, engineers, and other VIPs to celebrate the official inauguration of the array and tour its facilities. I was there along with 11 other journalists from around North America as guests of the National Radio Astronomy Observatory.
Overview of the telescope's technical capabilities, science goals, and history were given by (from left to right) Michael Thorburn, Head of the ALMA Department of Engineering, Pierre Cox, incoming ALMA director, Thijs de Graauw, current ALMA director, Al Wootten, ALMA Program Scientist for North America, and Ewine van Dishoeck, Professor at Leiden University and former ALMA board member.
The ALMA control room is the hub of activity at the "low site" or Operations Support Facility. From here, telescope operators manage and control all array operations and conduct observing runs. Astronomers who win time on the telescope through a merit-based proposal process do not actually travel to the site or control the telescope in real time. Instead, as with other radio interferometers, they prepare observing scripts based on what science they want to achieve, and their scripts are then scheduled and run by ALMA staff. The data is then made available to the astronomer for a proprietary period of one year, when it is then released to the public.
Everyone gets into the spirit of ALMA, which in Spanish actually means "soul," as an art contest was held for local children. Featured here are some of the submissions and several winners in the six to nine year old group.
54 of the final 66 antennas were at the "high site" or Array Operations Site, at an altitude of 16,500 feet. The 12-meter dishes are contributed by partners in Europe, North America, and East Asia, whereas several smaller, 7-meter dishes from East Asia make up a compact array in the center. The completed array will eventually have the capability of expansion by moving the antennas to different concrete "pads" spread around the Chajnantor Plateau. With a baseline, or distance between antennas, of up to 14 kilometers, ALMA will be able to obtain resolution ten times better than that of the Hubble Space Telescope.
Reporters were allowed a peek at the massive correlator behind glass in the second highest building in the world. The correlator is the computer that brings together signals from all the antennas so that the astronomer can make an image using the full array. We received a thorough explanation of its working from correlator engineer Alejandro Saez who has spent time constructing in in Charlottesville, Virginia, and at the high site in Chile. The correlator has the processing power of 3 million laptops as it has to make calculations for up to 1,125 antenna pairs billions of times per second.
The antennas actually put on a show for us during our three hour tour of the high site, slewing, or moving, back and forth. These antennas are built for perfection, or as close to it as one can come. These sturdy, yet flexible machines must maintain a dish surface accuracy of the width of a human hair and pivot back and forth between a target source and calibrator source on the sky every ten seconds.
Taking a hundred or so journalists to a site at 16,500 feet (5000 meters) altitude is quite risky business. Everyone must pass a basic fitness exam to be cleared for access, though employees must endure a much more rigorous process involving a stress test and heart monitoring to work on site. A team of diligent paramedics were there to hand out oxygen bottles and check for signs of altitude sickness. Here, I got my pulse checked in an ambulance after running around like an excited child a bit too much.
The "front end" of a radio telescope is the place where radio light that is collected by the dish is received, amplified, and transferred to the next stage for digital processing. The large blue drum is a cryostat and holds the most sensitive electronics in the telescope at a cold 4 Kelvin using liquid helium. The silver circles are the actual windows into the feedhorms, the first stage where radio light passes into the front end. Don't think those metal plates are transparent? They are to the radio light that ALMA receives.
Just one of ten sets of electronics that can fit inside those blue drums are on display here. Various stages of the system are cooled to difference temperatures, and engineers needs to wear special gloves and shirts when handling these so that they do not impart a spark of static electricity that could ruin a sensitive (and expensive) piece of equipment. The superconducting receivers used by ALMA are state-of-the-art and were developed specifically for this purpose.
How do you move a giant antenna? You build a giant antenna mover. The on-site guests were treated to an amazing site when one of the two antenna crawlers rumbled down a huge dirt road to pick up one of the dishes that is still under testing. Otto and Lore, as the crawlers are named, have to pick up each 100-ton antenna and place them down on their pads with millimeter accuracy. They move the antennas from the Operations Support Facility up to the high site and back and will be used to change array configurations to change the telescopes resolving power.
An enormous ring of dust and gas encircling a distant star may be forming planets at this very moment, based on what one Japanese team recently found in their observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
The ring, which surrounds the star HD 142527 over 456 light-years away in the southern constellation Lupus, is asymmetric in that it has a portion that is noticeably denser than the rest. This northern region, which shines brightly for ALMA in submillimeter-wave radio emissions, is located incredibly far from the star itself — about 22 billion kilometers, or five times the distance between the sun and Neptune.
“We are very surprised at the brightness of the northern side,” said Misato Fukagawa, the leader of the team and an assistant professor at Osaka University. “The brightest part in submillimeter wave is located far from the central star, and the distance is comparable to five times the distance between the Sun and the Neptune. I have never seen such a bright knot in such a distant position.”
A “bright knot” indicates the densest clustering of material in that portion of the ring — just the right kind of scenario to spark the formation of protoplanets, based on current models.
“When a sufficient amount of material is accumulated, planets or comets can be formed here,” Fukagawa added.
This is also the first firm evidence of planetary formation observed so far from the central star in a protoplanetary disk.
Based on measurements of the dense knot’s submillimeter emission strength and temperature, Fukagawa’s team concludes that either rocky planets or giant Jupiter-sized worlds are actively forming around HD 142527.
While gaps in the protoplanetary disk around this star have previously been observed, indicating the likelihood of planetary formation, this is the first time direct observations have been made within the internal part of the dust ring itself.
Watch an animation of the HD 142527 system below:
These findings put one more card in the deck of what astronomers know about how planets form around other stars — and thus how planets in our own solar system probably formed as well.
Also, because of its particular sensitivity to radio waves emitted by cold clouds of gas and dust, ALMA is the perfect instrument with which to investigate protoplanetary disks.
“HD 142527 is a peculiar object, as far as our limited knowledge goes,” said Fukagawa. “However, other asymmetrical protoplanetary disks have been discovered since the early ALMA science operation started. Our final goal is to reveal the major physical process which controls the formation of planets.”
Source: ALMA press release
Top image: Artist’s impression of the disk around HD 142527. Credit: NAOJ