ALMA reveals ghostly shape of 'coldest place in the universe'

Oct 24, 2013
ALMA reveals ghostly shape of 'coldest place in the universe'
The Boomerang Nebula, called the "coldest place in the Universe," reveals its true shape with ALMA. The background blue structure, as seen in visible light with the Hubble Space Telescope, shows a classic double-lobe shape with a very narrow central region. ALMA's resolution and ability to see the cold molecular gas reveals the nebula's more elongated shape, as seen in red. Credit: Bill Saxton; NRAO/AUI/NSF; NASA/Hubble; Raghvendra Sahai

At a cosmologically crisp one degree Kelvin (minus 458 degrees Fahrenheit), the Boomerang Nebula is the coldest known object in the Universe – colder, in fact, than the faint afterglow of the Big Bang, which is the natural background temperature of space.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope have taken a new look at this intriguing object to learn more about its frigid properties and to determine its true shape, which has an eerily ghost-like appearance.

As originally observed with ground-based telescopes, this nebula appeared lopsided, which is how it got its name. Later observations with the Hubble Space Telescope revealed a bow-tie-like structure. The new ALMA data, however, reveal that the Hubble image tells only part of the story, and the twin lobes seen in that image may actually be a trick of the light as seen at visible wavelengths.

"This ultra-cold object is extremely intriguing and we're learning much more about its true nature with ALMA," said Raghvendra Sahai, a researcher and principal scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and lead author of a paper published in the Astrophysical Journal. "What seemed like a double lobe, or 'boomerang' shape, from Earth-based optical telescopes, is actually a much broader structure that is expanding rapidly into space."

The Boomerang Nebula, located about 5,000 light-years away in the constellation Centaurus, is a relatively young example of an object known as a . Planetary nebulae, contrary to their name, are actually the end-of-life phases of stars like our Sun that have sloughed off their outer layers. What remains at their centers are white dwarf stars, which emit intense that causes the gas in the nebulae to glow and emit light in brilliant colors.

The Boomerang is a pre-planetary nebula, representing the stage in a star's life immediately preceding the planetary nebula phase, when the central star is not yet hot enough to emit enough ultraviolet radiation to produce the characteristic glow. At this stage, the nebula is seen by starlight reflecting off its dust grains.

The outflow of gas from this particular star is expanding rapidly and cooling itself in the process. This is similar in principle to the way refrigerators use expanding gas to produce cold temperatures. The researchers were able to take the temperature of the gas in the nebula by seeing how it absorbed the radiation, which has a very uniform temperature of 2.8 degrees Kelvin (minus 455 degrees Fahrenheit).

"When astronomers looked at this object in 2003 with Hubble, they saw a very classic 'hourglass' shape," commented Sahai. "Many planetary nebulae have this same double-lobe appearance, which is the result of streams of high-speed gas being jettisoned from the star. The jets then excavate holes in a surrounding cloud of gas that was ejected by the star even earlier in its lifetime as a red giant."

Observations with single-dish millimeter wavelength telescopes, however, did not detect the narrow waist seen by Hubble. Instead, they found a more uniform and nearly spherical outflow of material.

ALMA's unprecedented resolution allowed the researchers to reconcile this discrepancy. By observing the distribution of carbon monoxide molecules, which glow brightly at millimeter wavelengths, the astronomers were able to detect the double-lobe structure that is seen in the Hubble image, but only in the inner regions of the nebula. Further out, they actually observed a more elongated cloud of cold gas that is roughly round.

The researchers also discovered a dense lane of millimeter-sized dust grains surrounding the star, which explains why this outer cloud has an hourglass shape in visible light. The have created a mask that shades a portion of the central star and allows its light to leak out only in narrow but opposite directions into the cloud, giving it an hourglass appearance.

"This is important for the understanding of how die and become planetary nebulae," said Sahai. "Using ALMA, we were quite literally and figuratively able to shed new light on the death throes of a Sun-like star."

The new research also indicated that the outer fringes of the are beginning to warm, even though they are still slightly colder than the cosmic microwave background. This warming may be due to the photoelectric effect—an effect first proposed by Einstein in which light is absorbed by solid material, which then re-emits electrons.

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Lurker2358
1 / 5 (17) Oct 24, 2013
Seems like a thermodynamic contradiction.

An exploding object colder than it's own environment,colder than the background of the universe itself?
Gawad
5 / 5 (9) Oct 24, 2013
Just like when you let gas out of a pressurized canister, the contents of the canister become colder than the surrounding environment. If the volume of a planetary nebula expands quickly enough the same thing will happen.
Q-Star
5 / 5 (13) Oct 24, 2013
Seems like a thermodynamic contradiction.

An exploding object colder than it's own environment,colder than the background of the universe itself?


Not at all. It is exactly what thermodynamics describes, the expansion of any gas will result in local cooling, just as the release of a compressed gas from a container. It's how your ac and refrigerator works.
antonima
1.3 / 5 (12) Oct 24, 2013
If a gas expands into vacuum it will not cool. Temperature is just the kinetic energie of an ensamble of molecules. If there is nothing to slow the molecules down (something they would do work on) their temperature will remain constant.
Q-Star
4.9 / 5 (14) Oct 24, 2013
If a gas expands into vacuum it will not cool. Temperature is just the kinetic energie of an ensamble of molecules. If there is nothing to slow the molecules down (something they would do work on) their temperature will remain constant.


Of course it will "cool". Temperature IS the kinetic energy of the "ensemble" of the molecules, but it not only dependent on the velocity of the molecules, the density of the entire "ensemble" constrains the the transfer of that energy. If not constrained by a rigid and isolating container, the energy will dissipate. Without a certain level of energy input from outside the cloud, the temperature will decrease as the thermal kinetic energy is converted to radiation during the process of particle collisions. This is why the article pointed out that this is only a transient state until the parent star starts adding additional energy input. This is a more rapid process when the density decreases / gas expansion unless there is energy being added.
Lurker2358
1 / 5 (20) Oct 24, 2013
Cooling something to less than the background temperature of the environment suggests a reversal of Entropy, which should not be possible at that scale in nature.
Zephir_fan
Oct 24, 2013
This comment has been removed by a moderator.
antonima
1 / 5 (10) Oct 25, 2013
Of course it will "cool". Temperature IS the kinetic energy of the "ensemble" of the molecules, but it not only dependent on the velocity of the molecules, the density of the entire "ensemble" constrains the the transfer of that energy. If not constrained by a rigid and isolating container, the energy will dissipate. Without a certain level of energy input from outside the cloud, the temperature will decrease as the thermal kinetic energy is converted to radiation during the process of particle collisions.


The thermal energy of the cloud should only decrease to the point where it matches the microwave background, which is still hotter than the cloud. So, radiative processes alone cannot account for all the cooling.. however while it is true that expanding gases cool, they will not cool when they expand freely in a vacuum because their kinetic energies remain constant. The only explanation is that the cloud itself may offer enough resistance to expansion to allow cooling...
antonima
1 / 5 (5) Oct 25, 2013
however, if the cloud itself is absorbing work from the expanding cloud, the overall balance will remain constant. But, it is also necessary to consider that the expanding gas will have to conquer the parent star's gravitational field. This requires energy too, which may be part of the cooling. Anyhow, it is very complicated for sure.
Q-Star
4.5 / 5 (8) Oct 25, 2013
The thermal energy of the cloud should only decrease to the point where it matches the microwave background, which is still hotter than the cloud.


Well don't take my word for it. Take a can of compressed CO2, available at any hardware store, and spray it out, and see if the temperature doesn't fall below the ambient room temperature. Below the temperature of the canned CO2 AND the room. If ya are really bold spray it on your hand for about 30 seconds or a minute.

(I would suggest that ya have already called the EMS to give ya a ride to the ER because ya fingers will be frozen, frostbitten and hurt like the devil and it will be hard to dial the number.)
cantdrive85
1 / 5 (15) Oct 25, 2013
Just like when you let gas out of a pressurized canister, the contents of the canister become colder than the surrounding environment.


Where's the "canister" or what exactly pressurizes this "gas"? What then releases this cloud? And why does this "gas" have a distinct hourglass shape, contrary to any physics of gas disbursement?
I'm under the impression that the ignorance of plasma processes by astrophysicists and especially laymen prevents them from seeing what would otherwise be obvious.
Gawad
4.2 / 5 (5) Oct 25, 2013
Where's the "canister" or what exactly pressurizes this "gas"? What then releases this cloud? And why does this "gas" have a distinct hourglass shape, contrary to any physics of gas disbursement? I'm under the impression that the ignorance of plasma processes by astrophysicists and especially laymen prevents them from seeing what would otherwise be obvious.


Jesus you hacks & cracks are something. You make plenty of big claims and you don't even understand basic, grade school gas laws.

Imagine a sealed piston with 1m^3 of air in its cylinder. The air inside and outside is at 300K. Apply mechanical force to the piston to increase the volume in it to 2m^3. The temp will drop to 150K, barring friction. And it will stay there until heat can bleed back into the now 2m^3 of air in the piston from the surroundings. Same thing would hold for initial conditions at 3K.

As to the hourglass shape it's typical and occurs because supernovas collapse and rebound from the poles first.
cantdrive85
1 / 5 (13) Oct 25, 2013
I can imagine a sealed piston all I want, I want to know where this astrophysical piston is at, and what caused it to release the pressure. BTW, gas laws are meaningless in regards to this plasma.
Gawad
4.3 / 5 (6) Oct 25, 2013
I can imagine a sealed piston all I want, I want to know where this astrophysical piston is at, and what caused it to release the pressure. BTW, gas laws are meaningless in regards to this plasma.


It's the central star. THAT'S your piston here. "The outflow of gas from this particular star is expanding rapidly and cooling itself in the process." Jesus, didn't you even bother to read the article???

BTW, gas laws are meaningless in regards to this plasma.


Can't drive, or think, or even read. FAIL
Thewise
1.9 / 5 (9) Oct 25, 2013
As gas spreads out into a vacuum then the is less energy per cubic volume and the temperature drops, until energy radiates from the surrounding environment to equalize.
"adiabatic expansion of gas"
barakn
5 / 5 (6) Oct 25, 2013
Gawad: There was no supernova.
Antonima: You would be right if there was no work being done - the temperature wouldn't change. I can hear the shocked gasps from the audience: "that can't be right! What about a refrigerator?" Read this source http://prettygood...cuum.pdf before you give me a 1. But work is being done. It's a two-step process. As the cloud expands into the vacuum, the fastest atoms/molecules escape and leave the rest behind. The bulk of the gas cools by "evaporation." This might lead one to suspect a hotter shell of gas around a cold core, but these faster objects are moving up a gravity gradient. They are doing work, converting kinetic energy into gravitational potential energy. They are slowing down and cooling.
Q-Star: Blackbody radiation intensity varies as T^4. At such cool temperatures, and considering the reverse flow of energy from the CMB, radiation is not an important cooling mechanism in this scenario
Q-Star
5 / 5 (7) Oct 25, 2013
Q-Star: Blackbody radiation intensity varies as T^4. At such cool temperatures, and considering the reverse flow of energy from the CMB, radiation is not an important cooling mechanism in this scenario


I didn't mean to imply that it was. Perhaps I was unclear, sorry for my poor choice of words. The temperatures cooler than the CMB are possible UNTIL the gas expansion slows enough for the cloud to start warming by equalizing with the CMB or heating from the star which is providing the material for the pre-planetary nebula.
Gawad
5 / 5 (5) Oct 25, 2013
@Barakn: Quite right, reading back I see that I did write "supernova" instead of star in my second post. Hourglass shapes are seen in both cases, but obviously the one involved here is unrelated to a supernova. In this case, in addition to material being blown off the shell, material jets out from the poles as a result of rotation and magnetic fields rather than as a result of a rebound from a catastrophic collapse. My bad. I suppose that just reinforces the point that one should never post in haste.
yyz
5 / 5 (4) Oct 25, 2013
A preprint of "ALMA Observations of the Coldest Place in the Universe: The Boomerang Nebula" is available here: http://arxiv.org/abs/1308.4360
GSwift7
3 / 5 (5) Oct 28, 2013
The thermal energy of the cloud should only decrease to the point where it matches the microwave background, which is still hotter than the cloud.


You know how some things don't absorb microwaves? Yeah, well, you know the answer to your question then. In the absense of any source of radiation that the material can absorb, it will just continue to radiate in whatever frequency bands it can, until it reaches equilibrium in that bandwidth range.
beleg
1.6 / 5 (7) Nov 03, 2013
@baraka
This is one of those rarest moments in time of commentary thread history worth remembering.
The insight of/from empathy worded for and from understanding misunderstandings.
beleg
1.9 / 5 (8) Nov 03, 2013
@Zephir_fan
You targeted me for your down voting today.
Why?
Zephir_fan
Nov 03, 2013
This comment has been removed by a moderator.
cantdrive85
1.8 / 5 (11) Nov 03, 2013
@Zephir_fan
You targeted me for your down voting today.
Why?


That is a stupid question. If you make stupid comments you must take the one votes. Just be glad they don't allow negative votes or you would really have something to cry about. But since you only make goofy remarks you should get goofy karma points.

* troll
Zephir_fan
Nov 03, 2013
This comment has been removed by a moderator.
beleg
1.8 / 5 (4) Nov 05, 2013
@Zephir_fan
In one day you decided all my comments were "goofy" and rated them one.
No one can help you.
Zephir_fan
Nov 05, 2013
This comment has been removed by a moderator.
beleg
1.6 / 5 (5) Nov 05, 2013
People who answer you want you to follow your own advice you give others who don't need it.
Zephir_fan
Nov 05, 2013
This comment has been removed by a moderator.
beleg
1.8 / 5 (5) Nov 06, 2013
You miss the whole point of following one's own advice.
You can not forbid someone's mouth.
You demand silence yet continue to be vocal yourself.
You see no conflict, contradiction or inconsistency in your behavior.
People who answer you will point this out to you.