This year the Ligo Interferomenter Gravitational-wave Observatory (LIGO) Scientific Collaboration announced the discovery of a potentially new type of object that fell into a black hole, of course never to be seen or heard from again! Black holes are always interesting, but in this case it is not the black hole that is in the spotlight.
Instead, it is that ill-fated infalling object that grabbed all the attention. This is because information was obtained that points to the discovery of the heaviest known neutron star.
Neutron stars should not be confused with ordinary stars we see in the sky. Stars are made of hydrogen and tend to shine in colors which our eyes can see. On the other hand, neutron stars are formed from the centers of massive stars. They are made of neutrons, and are very dark against the night sky.
These dim neutron stars are also densely-packed: so much so that a single teaspoon would weigh as much as Mt. Everest. Remarkably, a neutron star does not collapse under its own weight because the neutrons push back on each other with great supporting strength.
But every system has a breaking point. It is thought that at a mass of around 2.5 times the mass of the sun, the stresses become so high that the neutron star is destroyed.
The neutron star just discovered in this study has an estimated mass that exceeds the value for the upper mass limit. Thus, it would appear that nature does not care what we think.
What can we conclude from this discovery? Might this object the new heavyweight champion of neutron stars? If so, then are there still heavier ones that further challenge our understanding of matter? Or, might the object have been a featherweight black hole all along?
We will get to add more to further our understanding of these most enigmatic objects as LIGO continues its survey of colliding neutron stars and black holes in years to come.
Is there a black hole in our backyard?
In Part One we discussed a proposed space mission called "Breakthrough Starshot," whose objective is to send a spacecraft the size of a grain of rice to the nearest star system, Alpha Centauri. All of us will be keen to get the first "up-close" photos of planets around a new star system. One would like to add that the journey may prove to be just as interesting as the destination.
This is because there is a growing consensus the nanocraft will pass by an object en route that is 5-10 times more massive than the Earth called "Planet 9." This enigmatic object was discovered by its pull on nearby metal-rich icy bodies (aka "dirty snowballs") in its immediate vicinity. Planet 9 is larger than expected for its placement in the outskirts of the Solar System, and on top of that has not yet been directly imaged. Because it may be dark and massive, it was recently proposed that Planet 9 might be a small and very old "primordial" black hole.
Wait a minute: if Planet 9 is a black hole, then will it suck up the entire solar system, including Earth?! While, it is the case that black holes do not let material that falls onto them escape, they are also not vacuum cleaners. So Earth is safe for now.
An interesting question to ask is can we confirm, or rule out, this seemingly preposterous idea? The Breakthrough Starshot nanocraft could potentially make a measurement that would support the black hole interpretation, but it would also be a challenge to obtain the necessary data set.
Another idea to search for icy bodies impacting onto Planet 9. In such a case, the impactor would heat up as it hits the accretion disk of the black hole and then would shine brightly in optical blue light just before disappearing into the black hole.
A new telescope coming on line soon called the LSST will have the ability to make such a detection and in doing so, give us some definitive answers as to what is lurking in our backyard.
Welcome ! For a little escape from the Solar System, let us take a look at the "Breakthrough Starshot" mission. The plan is to send a spacecraft to the nearest star apart from the Sun, Alpha Centauri, and to make that journey in only 20 years. This should impress you because the only objects deliberately launched from Earth that have left the Solar System, the Voyagers 1 and 2 satellites, require 200,000 years to achieve the distance of this nearest stellar neighbor, Alpha Centauri.
The actual spacecraft must be a very light one gram, or the weight of a single raisin. This feather-light construction already sounds like a tall order, but, recall that the processor of a cell phone has significant computing power yet is not much more than a factor of ten times more massive than what is required. Moving along, this "nanocraft" must also be able to travel at breakneck speeds of about one-tenth the speed of light, or 110 million km/hr (70 million mph). While no such satellite yet exists, the chosen approach for going fast is to attach a sail that "catches" a beam of laser light, rather like a sailboat mainsail that catches the wind.
On arrival to Alpha Centauri, this flying cell phone will take photos of Alpha Centauri and its planetary system and send them back to Earth. Having said that, in this case the journey will be as interesting as the destination. This is because the nanocraft may pass near to other objects along the way, such as the object in the outer Solar System that was proposed to exist by its gravitational influence on smaller icy bodies, but has not yet been detected. The most natural explanation is that this so-called "Planet 9" is, as the name implies, a massive planet. It has also recently been proposed that "Planet 9" may be a small black hole. Stay tuned for the next installment in which I will discuss this interesting second possibility that a small black hole lurks in the outer Solar System.
You may have heard the news from NASA that the James Webb Space Telescope (JWST) will suffer a delay in its launch date to March 30, 2021? In short, the sophisticated spacecraft plus solar shields were not quite up to specifications, requiring additional time for testing.
The JWST is the most celebrated telescope in the making. It is the much-touted "replacement" for the aging (26 year old) Hubble Space Telescope, yet this is hardly a fair comparison. The JWST will have seven times the collecting area of its predecessor and more sophisticated instruments which will enable us to see 13 billion years into the past. This is remarkable as the universe is only 13.7 billion years old. A significant challenge arises because unlike the Hubble Space Telescope, the JWST will not be serviceable. It has to survive the agitation of liftoff in a rocket, operate in the bitter cold of space, protect the sensitive astronomical instruments from damaging sunlight, and send data back to Earth on the first try. This is intense.
The design is broken down into two parts: (1) the science instrumentation, and (2) the spacecraft plus solar shields. Scientists across Europe, Canada and the U. S. constructed and tested the four sophisticated scientific instruments. In fact, I was lucky enough to get to serve on the instrument test-team of two of the instruments on two different continents. These are the Mid Infrared Instrument in Europe and the Near Infrared Camera (NIRCam) in the U. S. I participated in cryogenic testing, which involved writing and running code to do quality checks on all aspects of operation to ensure that the physical parts will work up to specifications in below freezing conditions.
In parallel, engineers at Northrop Grumman focussed on constructing the complicated solar sun shields as well as the spacecraft within which the science instrumentation will reside.
In general, problems tend to arise at juncture points, and the story relevant to JWST is no different. It was exactly when the science instrumentation and spacecraft came together that it was discovered that the latter was running a bit behind schedule. In particular, up to 70 fasteners on the spacecraft needed to be tightened up, and the solar shields, which are the sizes of tennis courts, needed to be repaired and to unfurl a bit faster. As we are told, the technology involved exceeds anything that has been done before. The only way forward is to "jump onboard" to help the spacecraft to catch up, which unfortunately will require additional time and finances. The unanimous mantra coming from NASA is that JWST is worth it! Afterall, JWST is 99% built and tested.
Innovation is costly and hard to put a deadline on, but we will do it, and as NASA will give the data freely to the public, the result will change the world.
As the saying goes, "There will be no wine, before its time."
We learn that there are four fundamental forces in nature: gravity, electromagnetism, and the strong and weak nuclear forces. One research group led by Dr. Lijing Shao from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has recently set out to test the possibility of a fifth force of nature.
We already know that gravity acts on matter. For example, gravity reliably pulls us to the Earth, keeps the Earth orbiting the Sun, and causes the Sun to orbit the center of the Milky Way.
The proposed new force would act preferentially on the dark matter. Dark matter is a component of the universe which dominates the mass of the universe, meaning that there is more dark matter than the protons, neutrons and electrons that we are made of, yet we cannot see it. This "fifth" force would pull ordinary matter towards the dark matter, or the other way around.
To search for evidence of a fifth force, Dr. Shao and his team studied a binary star system consisting of a pulsar and a white dwarf in orbit about each other. These two "degenerate" stars are so densely packed that their gravity is very high too, making them excellent candidates to study the forces pulling on them.
This experiment must be done by observing these objects in space, as degenerate material cannot be placed in a terrestrial lab. For example, a single teaspoon of a pulsar would fall through the Earth!
If a fifth force exists, then there would be a different pull on the denser pulsar relative to the "lighter" white dwarf. This should result in a detectable change in their orbits which was not seen. While this experiment did not show the anticipated change, this will not stop us from reaching out to understand the nature of dark matter.
Astronomers recently witnessed yet another ho-hum explosion of a star, or so they had thought..
Stars are fairly common near the centers of pairs of colliding galaxies, as are supermassive black holes. What happens when the two objects approach each other? The story begins when the star that is central to this week's story appeared to fall right on top of a black hole, at which point it released large amounts of X-rays.
This signature is typical of an exploding star, which is also a relatively common phenomenon in the centers of galaxies. On tracking this supernova over a ten-year period, however, the star did not show the attributes typical of others. It did not fade away over time as its energy dissipated, but instead formed into a long radio jet similar in appearance to a jet trail of an airplane passing overhead.
According to the results of a long-term study led by Seppo Mattila of the University of Turku in Finland, and Miguel Perez-Torres of the Astrophysical Institute of Andalusia in Spain, the answer to the mysterious circumstances of this stellar death is far from pedestrian.
By analyzing the radio jet and other observations taken in infrared colors, or heat, they discovered that the black hole that neighbored the ill-fated star was not a passive observer of the supernova. Rather, the scenario that fits the data best is that a portion of the star was consumed by the supermassive black hole, while another portion was stretched like taffy by the black hole into a long spaghetti-like stream of stellar material which we now see as the radio jet.
This is a rare detection of what astronomers call a "tidal disruption event," in which a black hole is caught disrupting a star. Such events may be relatively common especially in the centers of galaxies, and also usually hidden from our view.
Do you ever wonder how the "bumps" in the path of the Sun affect our weather? Probably not, and it certainly is not the leading story in the evening weather report. To the credit of meteorologists, this is because the Sun rarely does come across any "bumps," or side effects of near collisions with other stars.
From time to time the Sun will approach very closely to other stars in its orbit around the Milky Way. By "close" we mean that another star will pass within about three light-years of the Sun, which for reference is less than the distance between the Sun and the nearest star.
For example, a close passage of the Sun with another star 65 million years ago may have shaken loose several of the trillions of comets surrounding our solar system. Some of these "freed" comets would be sent hurtling into the inner solar system, where one of them could strike the Earth. In this scenario, on that one fateful day, the aftermath of the giant impact killed the dinosaurs.
Today, astronomers are able to search for new stars that may invoke other "doomsday" cometary showers, thanks to results arriving from the GAIA satellite. GAIA is a ne satellite that specializes in making exquisite measurements of star positions.
A team led by astronomer Bailer-Jones from the Max Planck Institute computed stellar orbits for 7 million stars.
They find that 25 stars will make closes approaches with the Sun within the next five million years. In fact, one of them, Gliese 710, is expected to hit that same repository of comets that led to the dinosaur's doom in 1.3 million years.
Just how close this star will come to us will determine when/if there will be another "perfect storm" which could lead to a new wave of extinction on Earth. Let's hope not...
Two of the nearest galaxies to the Milky Way, the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), are easily spotted by eye in the southern hemisphere. Sometimes shortened as "The Clouds," these much smaller and irregular-shaped "dwarf" galaxies orbit about the Milky Way, and will eventually be assimilated by it.
We have known for a while now of a column of hydrogen gas and stars that connects these two dwarf galaxies. But therein also lies the mystery: where did this stream of material come from? The two close contenders are: close fly-bys of the Clouds with the Milky Way, or close fly-bys of the LMC with the SMC.
Clues to solve this mystery come from studying the stars near the outer edges of The Clouds, which are held more tentatively as a result of the weaker gravitational pull.
Astronomer Dougal Mackey and collaborators (Australian National University) have undertaken a census of stars in the outskirts of the LMC and SMC as a part of a larger project called the "The Dark Energy Survey." The result of their census is changing the way we think about The Clouds.
Their census revealed that the stars separate out into two populations: an "intermediate age" 1 billion year one, and an "ancient" approximately 11 billion year one. In other words, they found different generations of stars to occupy different locations within the SMC, as if the stars followed zoning laws requiring older stars to live in the stellar equivalent of "retirement" communities.
This result hints that this "Magellanic Stream" may not be a result of a close approach to the Milky Way, but rather may have been a feature of the The Clouds for billions of years.
In a study led by Dr. Christian Wolf and reported in the Publications of the Astronomical Society of Australia, a black hole was just discovered that is consuming material at a record-breaking rate of one star every 2-3 days.
Dr. Wolf and his team found this black hole by searching for objects in the sky that do not move. Hyper-achieving black holes are very small and point-like, so can often be initially confused with stars. Side-by-side, the distinguishing feature is that only the stars are near to us. The implication is that over a period of years or decades only the stars will move across the sky.
But, once a distant object with an "active" black hole is found, what is going on there? Why is it shining so brightly?
One can imagine an assembly line that carries stars along it one-by-one. Each time a star drops off of the conveyer belt "at the end of the line," the star collides with the hot and fast moving collection of gas surrounding the black hole. This "accretion disk" takes in the doomed star which by now is stretching like taffy and heating up to the point that it emits X-rays and gamma-rays. Some of this high energy radiation shoots out of the black hole.
As a result of emitting radiation, it gives us a chance to find and study these objects which otherwise would be utterly dark.
This black hole that was just found shines with a brightness that is equal to about 10,000 times that of all the stars in the Milky Way combined. If we could relocate this object to the center of the Milky Way, then this monstrous object would appear in our night sky with a brightness equal to ten full moons.
This would disrupt the lives of nocturnal creatures on our planet, but this problem would be minor. The incident X-ray emission would be sufficient to irradiate all life on Earth. Fortunately, the black hole resident in the center of our galaxy is relatively calm. Indeed gluttony is an attribute of supermassive black holes typically associated only with sources existing very far away and a long time ago.
Professor Stephen Hawking wrote one final paper which is published posthumously. In this new paper, Hawking and collaborator Professor Thomas Hertog conclude that our Universe sprung from a larger state or "multiverse" that is not infinite.
Let us understand what this is all about by stepping back about 13.7 billion years in time. In these early days there is various evidence that our young Universe experienced a rapid period of growth called "inflation." A very short time later, the inflation stopped and calmed down into the more gentle mode of expansion plus acceleration we see in our Universe today. But what is the situation beyond our Universe, in the multiverse, and how does it behave?
The prevailing idea is that inflation is a normal attribute in the multiverse, such that the multiverse is expanding all the time at exponential rates in state called "eternal" inflation.
From time to time, a universe such as our own emerges, and potentially even an infinite number of universes arise each with a different set of physical laws. But Professor Hawking was never a fan of the multiverse.
Hawking and Hertog set out to understand better this significant problem on the starting assumption that relativity physics was not important in the early periods of inflation. As such, they were justified to consider that only quantum theory was the dominant physics. They then introduced the approximation that the multiverse is empty, meaning that it has no matter or energy. They went on to impose a shape of this larger entity, and removed the dimension of time from their equations altogether, as time has no meaning in a state not subject to relativity physics.
Their conclusion is that we still live a multiverse, but it is no longer infinite with infinite physics and infinite possibilities. But, as Douglas Adams tells us, it is still "mind-bogglingly big."
Black holes are hard to point to because they are...black.
Nevertheless, we did find out that there is a supermassive black hole at the Milky Way's center. It has a mass that is greater than that of the Sun by factors of tens of millions.
We arrived at this conclusion by watching what individual stars do that are very near to the Galactic center. These ill-fated stars describe oval-shaped orbits as if they are waltzing about some invisible central object.
Recent studies using sophisticated computer simulations are showing that about ten supermassive black holes should be lurking somewhere in galaxies the size of the Milky Way. Only one of these monsters would be situated at the very center (the one we found), while the others would orbit the galaxy at distances that are large compared to the Sun's distance from the Galactic center (whew), and far above or below the Galactic plane.
Fortunately, we are situated exactly in the plane in a relatively dull and unregarded ``suburb" of a spiral arm.
So do we have a chance to detect these other supermassive black holes in the Milky Way, if they exist? Black holes are impossible to see directly unless they are actively consuming some other object.
One idea that comes to mind is that we can discover black holes indirectly, by watching the effect they have on the light coming from the objects that happen to be behind them.
Black holes, afterall, are just like all other massive objects in that they the bend light around them. Shining a light near a black hole (but not into the black hole) will have the curious effect that the light appears to emerge from the other side. As an analogy, it is as if when you shine a flashlight onto a friend, that light would bend around your friend's body and appear to emerge from other side!
By monitoring millions of stars about once per week for evidence of this "light bending" effect, one can in principle locate these giant objects. To date no one has
found another supermassive black hole in our Galaxy. The best observatory to begin a search for such hidden
monsters is probably the Large Synoptic Sky Telescope (LSST) which is currently under construction in Chile.
There is a release of new astronomical data by the European Space Agency satellite called "Gaia." The main purpose of GAIA is to report accurate distances to stars
in the Milky Way. GAIA does this by measuring parallaxes.
This method relies on measuring what we might colloquially call "perspective." The idea is that a high precision snapshot of a nearby star will make a pattern on the sky with respect to its fixed stellar neighbors. If you then wait for six months and take another snapshot image of that same nearby star, you will see a slightly different pattern.
The Difference between the two images is called parallax.
Physically, what happens is that view of a nearby star against the background of fixed stars change when the Earth is one one side of its orbit compared to when the Earth is on the other side of its orbit. Similar an artist will paint a completely different picture of the same room depending on which corner the artist sits down.
The ancient Greeks attempted to measure parallaxes to nearby stars 2500 years ago, but failed. As a result, these scientists concluded that the Earth must be at the center of the Solar System. It was simply not realized at that time that even the nearest stars are so distant that our eyes cannot discern this difference in parallax (or in perspective).
The first parallax measurements would have to wait until the 19th century. But by this time we had already adopted the Sun-centered Solar System and figured out that the apparent lack of parallax was an indication of vast distances between us and the stars.
Moving forward to the 21st centure, what GAIA can bring us is parallax measurements not just of the nearest stars, but of 1.7 billion stars. Put another way, GAIA measured the distances to about one percent of the stars in the Milky Way.
Because many measurements were made over a five year period, this gives us the ability also to measure the motions of stars and the orbits of clumps of densely-packed stars called globular clusters. This is leading to a better understanding of our place in the Galaxy, and the data are offered for free to the public.