Tag: Brown Dwarfs

Astronomy News for August 2023: A cold Brown Dwarf star is found to be broadcasting radio waves and how Astronomers took a picture of the Milky Way, using Neutrinos instead of light!

We humans like to place the objects we find into distinct categories, male or female, dog or cat, living or non-living. Nature doesn’t really work that way however, the edges between different classes of objects are often quite fuzzy. Take stars and planets for example, back in my post of 22 September 2021, I discussed an relatively new class of objects called brown dwarfs, objects that are too heavy to be planets, but too light to be stars.

Brown Dwarfs are too big to be planets but too small to ignite the fusion processes that power regular stars. (Credit: EarthSky)

Strictly speaking brown dwarfs do not have enough mass to cause the pressure and temperature at their core to ignite the process of hydrogen fusion. They are larger than planets however and do emit some infrared light because the gasses they are made of continue to collapse due to gravity and that shrinking generates heat.

Strictly speaking the planet Jupiter is actually emitting a little more energy than it receives from the Sun because even after 4 billion years it is still shrinking. (Credit: European Space Agency)

One of the smallest, and coolest brown dwarfs ever discovered is known as WISE J062309.94-045624.6, (I’ll just call it J06 from now on) which is located about 7 light years from our solar system. The size and mass of J06 are only approximately known, its diameter is between 0.95 and 0.65 that of Jupiter while it’s mass is at least four time Jupiter’s, but not more than 44 times. We do have a rather accurate measurement of it’s surface temperature however, around 425ºC making it about as hot as a wood burning fireplace.

The Wide-Field Infrared Survey Experiment or WISE space telescope searches the sky for objects that are only emitting light in the infrared. (Credit: Wikipedia)

Being so cool it was something of a surprise therefore when observations of J06 by the CSIRO ASKAP radio telescope in Western Australia showed that the dwarf was broadcasting periodically at frequencies between 0.9 and 2.0 Giga-Hertz (That’s between 900 million and 2 billion cycles per second). These observations were later confirmed with the Australia Telescope Compact Array and South Africa’s MeerKAT telescope.

Unlike the images we get from Hubble or ground based telescope this is the sort of data we get from radio telescopes. These are some of the actual measurements from J06. (Credit: IOPscience-Institute of Physics)

The time period for the radio emissions was found to be about 1.91 hours which is thought to be the time it takes the dwarf to rotate on its axis, its day that is. An analysis of the data from J06 by researchers at the University of Sydney, including lead author Ph.D. candidate Kovi Rose has led to the conclusion that the dwarf possesses a magnetic field of greater than 700 gauss that is generating the radio emissions.

University of Sidney Ph.D candidate Kovi Rose. (Credit: Cosmos Magazine)

Only a small number of Brown Dwarfs have been discovered so far by astronomers and there is much we don’t know about this class of celestial objects. Only by finding more dwarfs, maybe by using their radio emissions to detect them, can we learn more about these objects.

South Africa’s MeerKAT antenna array is becoming one of the centers for the study of Brown Dwarfs. (Credit:

Unlike normal stars, Brown Dwarfs are studied by observing them in the infrared or radio portions of the electro-magnetic (EM) spectrum. One hundred years ago such observations could not have been carried out simply because the instruments needed to detect infrared and radio energy did not exist. Today however astronomers also have instruments that allow them to observe in the Ultra-Violet and X-ray portions of the EM spectra so that we can “see” the Universe in those lights as well.

Since X-rays are quickly absorbed by out atmosphere astronomers have to study them using space telescopes like the Chandra X-Ray probe shown here. (Credit: NASA)

More than that, today astronomers can even make observations of the Universe using Cosmic Ray particles and Gravity Waves, see my posts of 14 June 2017 and 22 October 2017. In fact every time that astronomers have found a new way to observe the Universe, a new form of energy with which to make astronomical studies, they have discovered whole new kinds of celestial objects and learned even more about the objects they already knew.

The LIGO observatory was the first to detect and study the Universe using gravity waves instead of light. (Credit: LIGO Caltech)

One type of radiation that astronomers that tried for a long time to employ are neutrinos, those ghost like sub-atomic particles that can pass through the entire Earth with hardly any of them interacting. That’s why neutrinos are so hard to use for astronomical observations, you need huge detectors, and lots of time, in order to catch just a few of them.

In order to capture just a few neutrinos you need huge detectors buried deep underground. (Credit: Nature)

That hasn’t stopped astronomers and astrophysicists from trying to use neutrinos however. The first time was a neutrino detector buried in the Homestake mine in South Dakota that was designed to detect neutrinos produced by the process of hydrogen fusion deep within the Sun. This experiment ran from 1970 to 1994 and taught us a great deal about both the Sun and neutrinos. Then, in 1987 the first supernova in our galaxy for over 300 years was detected and just as astrophysicists had predicted the Sudbury neutrino experiment detected about a dozen neutrinos from the distant event.

Buried in a massive glacier in Antarctica the Ice Cube neutrino detector is by volume the largest scientific experiment ever built. (Credit: Ice Cube Neutrino Observatory)

Now astronomers have constructed the largest, in terms of volume, experiment ever in the ice covered continent of Antarctica. The Ice Cube Telescope as it is known uses the fact that when a neutrino does interact with more normal matter it causes the emission of a few photons of light, photons that can travel a considerable distance through the Antarctic ice.

The scientists who operate Ice Cube live right above their instrument in this building near the south pole. (Credit: Wikipedia)

The Ice Cube Telescope was constructed with a full cubic kilometer of glacial ice near the Amundsen-Scott South Pole Station. Drilling holes down into the ice scientists buried over 5,000 light detectors so that they could detect the light generated by any neutrinos that were absorbed in that cubic kilometer of ice. Despite its huge size the Ice Cube detector still only captures a small number of neutrinos every day so, like taking a picture in very low light, in order to form any kind of image a long exposure time was required.

Taking a picture at night or in any low light conditions requires a time exposure like in the image here. (Credit: Visual Wilderness)

In fact it took over 10 years to collect 60,000 neutrino generated collisions and a special computer algorithm in order to form the first ever neutrino image of our Milky Way galaxy. Researchers from Drexel University’s Department of Physics Naoko Kurahashi Neilson, Associate Professor along with graduate student Steve Sclafani performed the processing that produced the image shown below.

The way our Milky way galaxy looks in radio (top), optical and gamma rays and now in neutrinos (bottom). (Credit: American Physical Society)
Naoko Kurahashi Neilson in her office at Drexel University and at the Ice Cube observatory in Antarctica. (Credit: UMKC WordPress)

This picture represents the birth of an entirely new kind of astronomy, neutrino astronomy. Right now we can only guess what neutrino images will tell us about the objects we already know about, but more importantly what new kinds of astronomical objects will be discovered using neutrinos.

For Decades Astronomers and Physicists have been thinking that Dark Matter is made up some kind of exotic sub-atomic particle. Maybe they’re wrong, maybe Dark Matter is made up of ordinary matter but in objects that don’t shine.

Let me begin today but reminding everyone of the problem of Dark Matter. Over the last 70-80 years as astronomers studied the dynamic behavior of the galaxies they found that the gravity of the objects that they could see, i.e. the stars that shined, was not sufficient to account for the way galaxies moved. There had to be some form of missing mass, some kind of dark matter in galaxies in order to explain their dynamics.

The Rotation speeds of stars in the spiral arms of galaxies, top curve, do not fit the expected speeds based on the matter that we can see, bottom curve. Dark Matter is the generic term for whatever was causing the difference. (Credit: Wikipedia)


Back in the 1980s when I was an undergraduate the ideas about Dark Matter had basically coalesced into two types of matter. These two classes of matter were given the corny names of Machos, meaning Mass Concentrations, and WIMPS meaning Weakly Interacting Massive Particles. Mass Concentrations were thought to be composed of ordinary particles like protons, neutrons and electrons and could be anything from small black holes to dark stars, given the name brown dwarfs, or even smaller objects like planets.

Too small to be a star yet too big to be a planet the question is, just how many Brown Dwarfs are there in the spaces between the stars? (Credit: Space News)


Now astronomers didn’t like the idea of having to look between the stars for small objects that didn’t shine by their own light, so they didn’t like Machos. Let’s face it telescopes are the main tool of astronomers and telescopes gather light from objects that shine like stars.

Telescopes gather a large amount of light, more than our eyes do, as well as magnifying an image. But objects that don’t emit or reflect light can’t be seen in a telescope no matter how powerful it is! (Credit: Meade)


On the other hand physicists loved the idea of WIMPs because at the time they were coming up theories of ‘Supersymmetry’ that predicted the existence of a large number of massive particles some of which could be WIMPs. So starting in the 1990s Machos were largely ignored while everybody went looking for WIMPs either in outer space or at the big atom smashers like the Tevatron at Fermilab or the new Large Hadron Collider at CERN.

Physicists are searching for ‘Physics beyond the Standard Model’. Some of that physics could be Dark Matter. (Credit: Phys.org)


Problem is that after thirty years of searching no particles that could be WIMPs have been found. And now it seems that the wind has shifted and maybe it’s time to take another look at Machos.

The James Webb Space Telescope is designed to observe the Universe in the infrared portion of the EM spectrum. This will enable it to search for both Brown Dwarfs and Rogue Planets helping astronomers get a better idea of their numbers. (Credit: Space.com)


For one thing astronomers have new, bigger, better instruments that are more capable of looking for objects that don’t shine at visible wavelengths. Just a few months ago I published a post about how astronomers are beginning to discover large numbers of Brown Dwarf stars, objects too big to be called planets but too small to ignite nuclear fusion in their cores so they do not shine like a star. See my post of 22 September 2021.

Just a few of the observatory domes that make up the European Southern Observatory high in the mountains of Chile. (Credit: Physics World)


Now a new study from the European Southern Observatory in Chile and Bordeaux University has announced the discovery of as many as 170 rouge planets, that is planets that do not orbit any star but rather move through the Milky Way all on their own. The rogue planets were discovered in a star forming region of the galaxy relativity close to our solar system in the constellations of Scorpius and Ophiuchus.

As one of the zodiacal signs Scorpius is a well known constellation but nearby Ophiuchus is also a very interesting part of the sky. The stellar nursery where the Rogue Planets were discovered lays between these two constellations. (Credit: International Astronomical Union)


It was the fact that the rogue planets were very young, and therefore still warm that enabled the astronomers to find them in the infrared region of the electromagnetic spectrum. Even so the astronomers at Bordeaux had to shift through observations accumulated over 20 years and still aren’t certain how many rogue planets they’ve found, the best estimate being 70 to 170 Jupiter sized worlds.

How many Rogue Planets are out there? It’s difficult to say because, once they’ve cooled down from their formation they are nearly impossible to find! (Credit: The Verge)


Still if the star forming regions in space are also producing large numbers of solitary planets who knows how many older rogue planets there could be between the stars. Could there be as many rogue planets as there are stars? Or maybe even more? Finding out just how many rogue planets there really are could be a difficult task, remember once the planet cools down like our earth did after a few million years they’ll be almost impossible to find.

Actual image of a Rogue Planet that is so young that it is still warm enough to be visible. (Credit: Colorado College Sites)


And there’s one more candidate for a Macho because the possibility that there could be large numbers of small, ‘primordial’ black holes in the Universe is once again being seriously discussed. These would be black holes with a mass that of a planet that formed in the first seconds after the big bang and have just been floating around ever since then. Such black holes would also be very difficult to find, unless of course one of them came inside our solar system.

Primordial Black Holes could have been formed a millionth of a second after the Big Bang. How many are out there? Your guess is as good as mine. (Credit: Owlcation)


So maybe we don’t need physics beyond the standard model in order to explain Dark Matter. If there are a lot more Brown Dwarfs than we ever imagined, more Rogue Planets and more primordial Black Holes maybe Dark Matter is just protons, neutrons and electrons in objects that don’t shine by their own light.
Machos may not be as exciting as WIMPs, but reality is what it is and after thirty years of failing to find any exotic elementary particles maybe we need to give Machos a rethink!

A Citizen Scientist discovers what could be the first of a new class of Brown Dwarfs. And what are Brown Dwarfs anyway?

Most people know that our Sun is pretty much a middle of the road star. Any star that is much more than 20 times the mass of our Sun is so big and unstable that it doesn’t last for very long. And any astronomic body that has much less than 1/20th our Sun’s mass won’t have enough pressure and temperature in its core to ignite hydrogen fusion, so they never shine as a star. Jupiter for example is the most massive of the planets, but since it only has 1/1000th the Sun’s mass it is a planet, not a star.

Our Sun, which is a middle sized star is about 1,000 times as massive as the large planet Jupiter. We now known that there are objects in between that we have christened ‘Brown Dwarfs’. (Credit: NASA)

Beginning in the 1960s astronomers began to wonder if there could be objects out in the galaxy that were too small to be stars yet too big to be planets, a class that was eventually given the name Brown Dwarfs. Such objects would have masses in the range of 10-80 times Jupiter’s mass and are often described to be ‘failed stars’.

Brown Dwarfs are too big to be planets but still aren’t massive enough to ignite nuclear fusion in their cores making them ‘failed stars’. (Credit: EarthSky)

Since they don’t shine in visible wavelengths like real stars, and the closest could be light years away Astronomers knew that Brown Dwarfs were going to be very difficult to find. Brown Dwarfs wouldn’t be totally dark however, even the smallest would have some heat left over from their formation while the heaviest could even have a small amount of heavy hydrogen, that is deuterium fusion going on inside them. Because of this Brown Dwarfs would be visible in infrared (IR) light.

There’s no reason why a Brown Dwarf couldn’t have a planet orbiting them but at the moment we’re having enough difficulty just finding Brown Dwarfs. (Credit: Owlcation)

Infrared astronomy is difficult here on Earth’s surface however, because even a tiny amount of water vapour in the air blocks IR light. In the 1960s there simply weren’t any IR telescopes and it wasn’t until the 1990s that a few IR space telescopes were launched into orbit and the first IR telescopes were built on the tops of the highest Andes Mountains, the driest place on Earth.

The high Atacama desert in the Andes mountains of Chile is the best place on Earth to do infra-red astronomy. (Credit: Aura Astronomy)

In 1988 a star designated as GD 165 was discovered to have a very small companion star, designated as GD 165B, during a search for white dwarf stars. The light of GD 165B was barely in the visible red portion of the visible spectra and astronomers wondered if it might be the first known Brown Dwarf. The debate over GD 165B’s status continued for almost a decade until new telescopes conducting the Two Micron All Sky Survey (2MASS) discovered over a hundred similar objects, and so Brown Dwarfs became a new class of celestial object.

What the Universe looks like at a wavelength of 2 Microns courtesy of the 2 Micron All Sky Survey (2MASS) (Credit: Infrared Processing and Analysis Center – Caltech)

Today Brown Dwarfs have been classified into two spectral types, both below the familiar O, B, A, F, G, K, M classes of normal stars. The larger Brown Dwarfs, which have a strong lithium line in their spectra, are classified as “L” type. Since true stars burn their lithium very quickly the presence of lithium in a spectra is indicative of a brown dwarf.

Normal stars are classified by their surface temperature as O, B, A, F, G, K, or M types with O being the hottest and M the coolest. Brown Dwarfs add two new classes L and T to the right. (Credit: SDSS SkyServer)

In time some brown dwarfs were discovered whose surface temperatures were cooler than the L type, so cool that methane was discovered in their spectra, even L type dwarfs are too hot for chemicals to exist. So a new class of Brown Dwarf, the “T” class was created. Presently astronomers have identified nearly a thousand L type and about 350 T type Brown Dwarfs.

Two classes of Brown Dwarfs are recognized by all astronomers while a new classification “Y” is still being debated. (Credit: Backyard Worlds)

Since Brown Dwarfs generate little if any energy by fusion they really have no stable “Main Sequence” period in their lives but instead just continue to get cooler and cooler, eventually becoming so cool that they no longer even radiate in IR wavelengths. For that reason it was thought that it would be very difficult if not impossible to detect a Brown Dwarf that was more than a few billion years old.

But they may just have found one by ‘Accident’, or at least citizen scientist Dan Caselden seems to have found one and his finding it really was an accident. Caselden had written a computer program to search for Brown Dwarfs in the data collected by the Near Earth Object – Wide field Infrared Survey Explorer (NEO-WISE) satellite. In particular Caselden was looking for objects so close to our solar system that they would appear to move slightly against the background of more distant starts over the course of six months or a year. (NEO-WISE conducts a complete survey of the entire sky every six months)

The Wide-field Infrared Survey Explorer (WISE) satellite has been given a new mission to search for Near Earth Objects (NEOs) making it now the NEO-WISE mission. (Credit: Wikipedia)

Caselden was checking out one candidate for a close Brown Dwarf when he noticed another object nearby that was moving even faster. Its spectra didn’t look like that of a Brown Dwarf but Caselden decided he’d check it out.

By day a Security Engineer in his spare time Dan Caselden is a new breed of computer astronomers. Seriously all of the satellites we’ve put into space are sending back so much data that even ordinary people, with a computer, can make important discoveries. (Credit: NASA Solar System Exploration)

Caselden’s discovery has now been given the official designation of WISEA J153429.75-104303.03 but it’s also known by its nickname of Accident. When examined more closely by powerful ground based telescopes Accident was found to be as cool as a T type Brown Dwarf but there was no trace of methane in its spectra. In fact there was no trace of carbon or any of the more massive elements like oxygen or sodium or iron. WISEA J153429.75-104303.03 appears to be made entirely of the elements hydrogen and helium.

If you’re interested in being a citizen scientist try checking it out on YouTube. (Credit: Twitter)

That would indicate that Accident is old, very old, ten billion years old or older. You see, shortly after the big bang, when the first galaxies began to form the matter in the Universe was almost entirely hydrogen and helium. The heavier elements, like those that make up planets and even our our bodies were created inside the nuclear furnaces of the first generation of stars some 10 to 13 billion years ago.

The first stars began to form only 100 million years after the Big Bang. At that time only the elements Hydrogen and Helium existed in any amount so the elements that formed the planets, and our bodies were forged in the cores of those first stars. (Credit: Futurism)

So Accident may be a Brown Dwarf that was formed at the same time as the very first stars. If that is so then WISEA J153429.75-104303.03 may hold secrets within it that relate to how the first stars and galaxies came into being. WISEA J153429.75-104303.03 could even be the first in an entirely new class of Brown Dwarfs. So I guess it will be no accident if astronomers pay a great deal of attention to it in the years to come.

Accident brings another question to mind. Just how many Brown Dwarfs are there out there in our galaxy? So far we have only found around two thousand but they are all rather close, within 100 light years. We are still only beginning to get a feel for how common they are.

Many of the Brown Dwarfs we know about are companions of more normal stars such as this one. (Credit: Universe Today)

We do know that there are a lot more middle sized stars like our Sun than big, bright ones like Vega, and there are a lot more small, dim stars like Barnard’s star or Proxima Centauri than middling stars like our Sun. If you extrapolate from those facts then there could be a lot more Brown Dwarfs in the Milky Way than all of the real stars put together.

On a clear night you can see thousands of nearby stars but how many Brown Dwarfs are out there that we can’t see? (Credit: Space Tourism Guide)

Think about that the next time you go out on a nice clear night to gaze up at the heavens.