# What would happen if a star passed through the barycenter of two binary stars?

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I was doing some research on Alpha Centauri A and B, and thought to myself: 'What would happen if something passed directly through the barycenter of these two stars?' I may theorise that a passing star will offset the barycenter with its gravity, sending the two stars in whatever direction it would go. I am not certain about this, nor am I certain that anyone has the answer. But if they do, please answer, I'd really like to know!

If we assume the binary pair have equal masses, then by symmetry a star passing through their barycenter at right angles to their rotation plane will not change their symmetry.

I did some simple simulations where a star with mass 0.1 flies through a binary in an originally circular orbit.

The first case is with an interloper moving at speed 20. It passes through, losing a bit of momentum to the binary, that now moves slowly in the same direction.

The second is an interloper moving more slowly, with speed 1. Now the binary moves along more, and the interaction causes a quasiperiodic oscillation in seimajor axis.

Just dropping the interloper with zero velocity makes it bound to the binary, oscillating back and forth, driving complex quasiperiodic or chaotic motion.

It is possible to make the pair scatter by throwing in a sufficiently heavy interloper with enough momentum that first drags the binaries close, transfers enough momentum to unbind the system, and then passes along.

Of course, if the direction is not exactly symmetric things can turn messy. Note that there are non-chaotic solutions too.

To sum up, interlopers can deposit energy and momentum, split binaries, or create chaotic tangles. But it is not the barycenter that is the important part.

No, a star passing through the barrycenter or anywhere between the stars or nearby wouldn't send the stars flying away nor would it cancel out anything. The effect would depend on how large your passing through star was, how fast it passed through and from what angle it approached, that is, how close it passed to each of the Alpha Centauri stars.

How much of a kick or push it gives each object would depend on the relative direction, speed and distance and the gravitation or mass of your passing star, so it might pull the stars closer together, it might push them father apart, but in that would just be adding a vector to the motion of the stars that was already present.

If you imagine all three stars have similar mass, which would be a normal thing to assume as a first approximation, and assuming the incident speed is larger than the orbital velocity (it likely would be, because it is getting pulled in), then the interaction would seem to be likely to happen with one of the stars in the binary, moreso than the other. So for a short time, those two stars would behave like two objects undergoing "Rutherford scattering." It would indeed depend sensitively on the details (especially the incident angle), but it does seem pretty likely to me that it would disrupt the initial binary. It's possible that the interloping star could even grab one of the stars into a binary with itself, leaving the other one behind, but if the star comes in fast, it seems pretty likely that the original binary will at the very least be made highly eccentric, and quite likely disrupted altogether. But yes, there's no substitute for an orbital simulation.

Now, it occurs to me you might be imagining the third star comes in along the axis of the original binary. In that special case, the incident star would have no effect at all if the original binary had two equal mass stars in a circular orbit-- it would simply speed up the whole initial binary toward it, and then return it to its original movement after it passes. But it wouldn't leave the stars moving-- it would erase its effect as it leaves, and all that would linger is an overall shift in the location of the barycenter. But it's a very special case there.

## Binary Stars and Double Stars

The sight of binary stars partnered together is stunning, especially when they have vibrant colours.

After the invention of the telescope in the 17th century, the true nature of the night's sky became apparent. What had been mere fuzzy blobs to the unaided eye now had formed, and suddenly a whole new world of nebular, galaxies and star clusters could be observed.

When telescopes were trained on the star an interesting discovery was made - not all the stars we see as single points with our eyes are in fact alone. Some were revealed to be two stars or maybe even more. Double stars and multiple star systems were discovered.

## Question what happens if a star spins it self faster than light?

No because they can't exist. Imagine trying to hang on at the edge of a merry-go-round (dia. = 10 ft.) spinning at 1 revolution per sec. Now increase that rotation to 31 million revs per sec.

Stars too would fly apart before they could even form if spin were just a fraction of light speed.

Oddly enough, in the past, it was deemed impossible for stars to form from clouds because all clouds have some rotation. Though these rotations are small, the cloud collapse is by 20 orders of magnitude, which means a star, when collapsed to a normal size, would have rotation speeds exceeding the speed of light. This greatly delayed the cloud collapse model for decades until it was determined that other events did allow the clouds to collapse.

#### Snowball Solar System

A star will centrifugally fragment long before reaching light speed rotation, which would be true even for compact stars like white dwarfs or neutron stars.

Here's what happens when a hydrostatic object spins up to the point of centrifugal fragmentation, which I suggest has actually happened in our solar system:

Multiple star systems evolve by means of 'orbital interplay', wherein the least massive components are 'evaporated', outward, while the more massive stars sink inward to form a core (or binary pair in the case of two massive stars). The principle is that of 'equipartition of kinetic energy', which tends to transfer kinetic energy from more-massive objects to less-massive objects in orbital close encounters.

Here's the kicker--not only do less massive objects acquire kinetic energy and angular momentum from more massive objects, but they are also induced to 'spin up', increasing their rotation rate. In a globular cluster with no net angular momentum, the angular momentum vectors are misaligned, causing no progressive spin up, but in a planar system, like a protoplanetary disk (where angular momentum vectors are aligned), I suggest that something very unusual can occur.

Imagine a high angular momentum protoplanetary disk where the central diminutive (brown-dwarf-mass) protostar is much, much less massive than the the surrounding disk, where an m=2 mode disk instability forms a twin-binary pair of disk-instability objects in orbit around the brown-dwarf central core.

Orbital interplay causes the twin protostars to evaporate the brown dwarf into a circumbinary orbit, as the twin protostars sink inward (conserving angular momentum) to form a stellar close binary pair, but if the commensurate spin up causes the brown dwarf to centrifugally fragment, I suggest that the fragmentation occurs in a very particular manor.

Spin up first causes the object to distort into an oblate sphere, but then something unusual happens. Self gravity takes over, and the oblate sphere distorts into a Jacobi ellipsoid, which progresses (with additional spin up) into a bar-mode instability, which centrifugally fails when the self gravity of the arms cause them to pinch off into a massive twin-binary pair orbiting a diminutive residual core, in a process I call, 'trifurcation'.

And 1st-generation trifurcation promotes 2nd-generation trifurcation, by the same equipartition principle, creating a set of twin-binary pairs in decreasing sizes, like Russian nesting dolls.

With multiple generations of trifurcation, I suggest a former binary-Sun (twin-binary disk instability objects) caused our former brown dwarf to undergo 4 generations of trifurcation, forming: (former)
- 1st-gen. -- former binary-Companion + SUPER-Jupiter residual core,
- 2nd gen. -- Jupiter-Saturn + SUPER-Neptune residual core
- 3rd gen. -- Uranus-Neptune + SUPER-Earth residual core
- 4th gen. -- Venus-Earth + Mercury residual core

Then binary-binary resonances resolved the system, causing eccentricity pumping that caused binary-Sun to capture the three sets of twin planets from binary-Companion forming this intermediate configuration, listed in increasing radial distance from the solar system barycenter :
Binary-Sun, Venus-Earth-Mercury, Jupiter-Saturn, binary-Companion, Uranus-Neptune, trifurcation debris disk. (Forget about Mars for now.) And hot classical Kuiper belt objects (KBOs) 'condensed' by streaming instability from the trifurcation debris disk.

Additional eccentricity pumping caused all binary pairs to separate, except for binary-Companion because the binary-Sun components spiraled in to merge in a luminous red nova at 4,567 Ma, forming a solar-merger debris disk which 'condensed' by streaming instability the asteroids, with live solar-merger-nucleosynthesis short-lived radionuclides (SLRs). And chondrites condensed later after the SLRs had largely died away.

Binary-Companion, with super-Jupiter-mass binary components, orbited the sun for almost 4 billion years between the orbits of Saturn and Uranus, but perturbation by the Sun caused the binary components to spiral inward over time, where the close-binary potential energy transferred to the heliocentric Sun-Companion orbit, causing the binary-Companion orbit to become increasingly eccentric over time, which also increased binary-Companion's heliocentric period.

The progressively-increasing heliocentric period caused its 1:4 mean-motion resonance to spiral out through the Kuiper belt, perturbing KBOs from about 4.1-3.8 Ga, causing the late heavy bombardment of the inner solar system.

And binary-Companion overran Uranus', orbit causing Uranus' severe axial tilt.

Finally, the super-Jupiter-mass binary components spiraled in to merge at 650 Ma in an asymmetrical merger explosion that gave newly-merged Companion escape velocity from the Sun, and the Companion-merger debris disk fogged the solar system, causing the Marinoan glaciation of Snowball Earth. And the earlier Sturtian glaciation of the Cryogenian Period was caused by the binary components progressively accreting their moons as they spiraled inward.

The 650 Ma Companion-merger debris disk condensed the cold classical KBOs, in quiescent low-eccentricity, low-inclination orbits, and possibly Ceres (with its low large-crater count and internal ocean, despite experiencing NO tidal heating), and possibly even Pluto (with its geologically-active surface despite its synchronous orbit with Charon, resulting in NO tidal heating).

By comparison, Grand Tack requires more variables to explain many-fewer solar system phenomena, and it's far less falsifiable. Grand Tack requires Jupiter to migrate in (to explain the configuration of the inner solar system) then migrate out (to explain the configuration of the outer solar system), with each maneuver requiring its own set of variables (depending on the fine tuning of the conveniently-disappeared protoplanetary disk), and it doesn't predict and can't explain our 3 sets of twin planets (Jupiter-Saturn, Uranus-Neptune, Venus-Earth) it can't explain the bimodal late heavy bombardment (where the 1:4 resonance first perturbed the Plutinos followed by the cubewanos) it can't explain the bimodal Snowball Earth episodes and it can't explain Uranus' severe axial tilt. (There's more, but that would just be piling on.)

In competition, the test may require reading a light curve. Light curves are graphs of light intensity, generally in a specific frequency range, with respect to time. This is very important for variable stars, as certain types of variable stars will have light curves with a specific shape. By measuring the light intensity of an object and generating a light curve, one can often determine what type of object it is.

Light curves are useful for both periodic and explosive variables. For periodic variables, the shape and pattern of cycles in the light curve often gives a significant clue as to the type of object. However, the shape of light curves from explosive variables is also very helpful in identifying novae and supernovae, especially Type Ia supernova. More information about the use of light curves with respect to Type Ia supernovae may be found on this page.

## Valuable insights as neutron star passed through stellar winds

Data recorded by NASA's Chandra X-ray Observatory of a neutron star as it passed through a dense patch of stellar wind emanating from its massive companion star provide valuable insight about the structure and composition of stellar winds and about the environment of the neutron star itself. A paper describing the research, led by Penn State astronomers, appears January 15, 2019, in the journal, Monthly Notices of the Royal Astronomical Society .

"Stellar winds are the fast-flowing material--composed of protons, electrons, and metal atoms--ejected from stars," said Pragati Pradhan, a postdoctoral researcher in astronomy and astrophysics at Penn State and the lead author of the paper. "This material enriches the star's surroundings with metals, kinetic energy, and ionizing radiation. It is the source material for star formation. Until the last decade, it was thought that stellar winds were homogenous, but these Chandra data provide direct evidence that stellar winds are populated with dense clumps."

The neutron star observed is part of a high-mass X-ray binary system--the compact, incredibly dense neutron star paired with a massive 'normal' supergiant star. Neutron stars in binary systems produce X-rays when material from the companion star falls toward the neutron star and is accelerated to high velocities. As a result of this acceleration, X-rays are produced that can inturn interact with the materials of the stellar wind to produce secondary X-rays of signature energies at various distances from the neutron star. Neutral--uncharged--iron atoms, for example, produce fluorescence X-rays with energies of 6.4 kilo-electron volts (keV), roughly 3000 times the energy of visible light. Astronomers use spectrometers, like the instrument on Chandra, to capture these X-rays and separate them based on their energy to learn about the compositions of stars.

"Neutral iron atoms are a more common component of stars so we usually see a large peak at 6.4 keV in the data from our spectrometers when looking at X-rays from most neutron stars in a high-mass X-ray binary system," said Pradhan. "When we looked at X-ray data from the high-mass X-ray binary system known as OAO 1657-415 we saw that this peak at 6.4 keV had an unusual feature. The peak had a broad extension down to 6.3 keV. This extension is referred to as a 'Compton shoulder' and indicates that the X-rays from neutral iron are being back scattered by dense matter surrounding the star. This is only the second high-mass X-ray binary system where such a feature has been detected."

The researchers also used the Chandra's state-of-the-art engineering to identify a lower limit on the distance from the neutron star that the X-rays from neutral iron are formed. Their spectral analysis showed that neutral iron is ionized at least 2.5 light-seconds, a distance of approximately 750 million meters or nearly 500,000 miles, from the neutron star to produce X-rays.

"In this work, we see a dimming of the X-rays from the neutron star and a prominent line from neutral iron in the X-ray spectrum--two signatures supporting the clumpy nature of stellar winds," said Pradhan. "Furthermore, the detection of Compton shoulder has also allowed us to map the environment around this neutron star. We expect to be able to improve our understanding of these phenomenon with the upcoming launch of spacecrafts like Lynx and Athena, which will have improved X-ray spectral resolution."

For Pradhan's post-doctoral work at Penn State under the supervision of Professor of Astronomy and Astrophysics David Burrows, Associate Research Professor of Astronomy and Astrophysics Jamie Kennea, and Research Professor of Astronomy and Astrophysics Abe Falcone, she is majorly involved in writing algorithms for on-board detection of X-rays from transient astronomical events such as those seen from these high-mass X-ray binary systems for instruments that will be on the Athena spacecraft.

Pradhan and her team also have a follow-up campaign looking at the same high-mass X-ray binary with another NASA satellite--NuSTAR, which will cover a broader spectrum of X-rays from this source ranging in energies from

"We are excited about the upcoming NuSTAR observation too," said Pradhan. "Such observations in hard X-rays will add another dimension to our understanding of the physics of this system and we will have an opportunity to estimate the magnetic field of the neutron star in OAO 1657-415, which is likely a million times stronger than strongest magnetic field on Earth."

## Weird dust clouds orbiting our galaxy’s central black hole may be weirder than we thought

At the center of our Milky Way galaxy sits a supermassive black hole — which astronomers named Sgr A* — with over 4 million times the Sun's mass.

But it's not alone. Lots of other stuff is there, too, orbiting that black hole, including stars, gas, and dust. Over time, we can see these objects move, held sway by the incredible gravity of Sgr A*. In fact, the motions of several stars have told us a lot about the black hole itself.

But there is another class of objects there, something just recently discovered, and it's not clear what they are. If a team of astronomers is right, they could be among the more bizarre objects in the galaxy: Binary stars that, under the fierce influence of the black hole, have merged to become, something else. Single stars, but weird ones.

The first of these objects, called G1, was discovered in 2005, and the second (G2) in 2012. They looked like dust clouds, compact clumps of material. But in 2014, G2 passed very close to the black hole, close enough that were it a simple cloud it would've been shredded by the huge tidal force of the black hole. Shockingly, it survived intact! Astronomers then speculated that it may be a cloud of dust surrounding a star, and the gravity of the star kept the cloud from dispersing. But without more examples it was hard to know anything more.

And that's where the new research comes in. Using the massive Keck 10-meter infrared telescope in Hawaii, the astronomers found four more objects orbiting the supermassive black hole that look very much like the first two.

Schematic diagram of the orbits of the G1-6 dust clouds around the galactic center. Left: a 3D representation where the current positions and directions of the objects are indicated. Right: Their positions and orbital motion indicated as viewed from Earth. Credit: Ciurlo et al.

Like the first two, they appear to be dust clouds, emitting light characteristic of such things. They also appear to have hydrogen gas in them, which glows in the infrared at a specific wavelength (called Brackett gamma at about 2.2 microns, well outside what the human eye can see). They're on elliptical orbits around the black hole with periods ranging from 170 to 1,600 years, but the orbits are pretty different from each other (different ellipticities and orbit planes) indicating they didn’t all form from a single object like a dust cloud that got torn apart into littler ones. Interestingly, they've all remained about the same brightness over the 13 years of observations, so they appear to be somewhat stable.

So they can't be simple dust clouds, as we knew from the G2 close pass of the black hole. Then what are they?

Artwork depicting dust clouds with stars embedded in them orbiting Sgr A*, the supermassive black hole in the center of the Milky Way. Credit: Jack Ciurlo

The astronomers turned once again to the idea that each may once have been a binary star system, two stars orbiting each other closely. About half the stars in the galaxy are in binary systems like this, so they're very common. Usually, especially for low mass stars, they can orbit each like this for billions of years, happily swinging each other around their common center of gravity.

But ones close to the galactic center have a supermassive problem: Sgr A*. If they get too close to it in their orbit, the tides from the black hole can affect them. In a nutshell, gravity gets stronger the closer you are to an object, and if that object is a black hole that gradient can be steep. As they approach, one star is a little closer to the black hole than the other and gets pulled on much harder. This stretches the orbit due to that change in gravity. When they finally move away from Sgr A* their orbit around each other can be significantly modified.

If this happens again and again, the two stars can be dropped so close to each other that they merge, becoming a single star.

V838 Monocerotis. Credit: Roberto Colombari / NASA / TheHubble HeritageTeam (AURA/STScI)

Mind you, this is a hugely energetic thing to have happen! We’re talking stars here. When they merge a lot of very powerful events occur, including the generation of a lot of dust: tiny grains of rocky or carbonaceous material. This dust expands around the star, forming a dense cloud around it.

That’s not just theory: We've seen it happen. The star V838 Monocerotis is an example of exactly this event. It's likely to be two massive stars that merged and blew out a huge cloud of dust. At some point in the recent past the star had an outburst of light, and as that pulse traveled through the cloud it illuminated different parts of it (it looks as if we’re watching the cloud expand, but in reality it's just the light moving through it that we see).

So are we seeing a half-dozen V838 Monocerotises * orbiting our galaxy's central supermassive black hole? It's certainly possible. The number we see fits, the idea that they are stars embedded in dense dust clouds fits, the dynamics fit (that is, getting binary stars around the black hole affected by its tides and merging is physically plausible), and we have an example of just such a beast (though not orbiting near the black hole V838 is about 2,000 light years from us, while we’re 26,000 light years from the center of the galaxy). In fact, there was a recent burst of star formation in the galactic center about 4–6 million years ago, which very well could have been when these binaries were born.

So this is pretty convincing to me. I’ll note I liked this idea even before G3–6 were found, so I'm inclined to see this as more support. And if it turns out they're not recently merged binary stars eructating clouds of dust, well, then that means they're something even more bizarre.

I'm certainly OK with that. When you're talking supermassive black holes, all manners of weird stuff become commonplace. So whatever these things are, they're cool, and well worth keeping an (infrared) eye on.

* Pluralizing the genitive case of a Greek word in an English manner is well beyond my linguistic skills. So I'm going with that.

A binary star is a star system of two stars that orbit around the central point, called the barycenter. In conversation, binary stars are sometimes casually referred to as double stars. Binary star systems or multiple star systems (3+ stars in orbit in the same system) are actually way more common than you might think.Continue reading “Binary Stars” Continue reading &rarr

Is it a bird? a plane? a superhero? No it&rsquos a Comet! Comet&rsquos are &ldquocosmic snowballs of frozen gases, rock and dust that orbit the Sun&rdquo. Comet&rsquos generally range from the size of 750 meters to 20 kilometers. Currently there are 3,717 comets known to man. Comet&rsquos form from dust particles combining to form icyContinue reading “Comet” Continue reading &rarr

## Meteorites, Comets, and Planets

### 1.02.1 Introduction

Traditionally, astronomers have studied the stars by using, with rare exception, electromagnetic radiation received by telescopes on and above the Earth. Since the mid-1980s, an additional observational window has been opened in the form of microscopic presolar grains found in primitive meteorites. These grains had apparently formed in stellar outflows of late-type stars and in the ejecta of stellar explosions and had survived the formation of the solar system. They can be located in and extracted from their parent meteorites and studied in detail in the laboratory. Their stellar origin is recognized by their isotopic compositions, which are completely different from those of the solar system and, for some elements, cover extremely wide ranges, leaving little doubt that the grains are ancient stardust.

By the 1950s it had been conclusively established that the elements from carbon on up are produced by nuclear reactions in stars and the classic papers by Burbidge et al. (1957) and Cameron (1957) provided a theoretical framework for stellar nucleosynthesis. According to these authors, nuclear processes produce elements with very different isotopic compositions, depending on the specific stellar source. The newly produced elements are injected into the interstellar medium (ISM) by stellar winds or as supernova (SN) ejecta, enriching the galaxy in “metals” (all elements heavier than helium) and after a long galactic history the solar system is believed to have formed from a mix of this material. In fact, the original work by Burbidge et al. and Cameron was stimulated by the observation of regularities in the abundance of the nuclides in the solar system as obtained by the study of meteorites ( Suess and Urey, 1956 ). Although providing only a grand average of many stellar sources, the solar system abundances of the elements and isotopes (see Chapter 1.03 Anders and Grevesse, 1989 Grevesse et al., 1996 Lodders, 2003 Asplund et al., 2005 ) remained an important test for nucleosynthesis theory (e.g., Timmes et al., 1995 ).

In contrast, the study of stellar grains permits information to be obtained about individual stars, complementing astronomical observations of elemental and isotopic abundances in stars (e.g., Lambert, 1991 ), by extending measurements to elements that cannot be measured astronomically. In addition to nucleosynthesis and stellar evolution, presolar grains provide information about galactic chemical evolution, physical properties in stellar atmospheres, mixing of SN ejecta and conditions in the solar nebula and in the parent bodies of the meteorites in which the grains are found.

This new field of astronomy has grown to an extent that not all aspects of presolar grains can be treated in detail in this chapter. The interested reader is therefore referred to some recent reviews ( Anders and Zinner, 1993 Ott, 1993 Zinner, 1998a, b Hoppe and Zinner, 2000 Nittler, 2003 Clayton and Nittler, 2004 Hoppe, 2004 Lodders and Amari, 2005 Lugaro, 2005 ) and to the compilation of papers found in Astrophysical Implications of the Laboratory Studies of Presolar Material ( Bernatowicz and Zinner, 1997 ). The book not only contains several detailed review papers on presolar dust grains but also a series of chapters on stellar nucleosynthesis. Further information on nucleosynthesis can be obtained from the textbooks by Clayton (1983b) and Arnett (1996) and from reviews by Käppeler et al. (1989) , Meyer (1994) , Wallerstein et al. (1997) and Meyer and Zinner (2006) .

## Did a close pass by an alien star system millennia ago rain down comets on the solar system?

70,000 years ago, a binary star system gave our solar system a pretty close shave, passing less than a light-year from the Sun. That's unusual on average stars are more like 4 light-years apart — in fact the closest known star to us about 4.2 light-years away.

Could this close stellar encounter millennia ago have affected the solar system in any way? The answer is…. maybe.

Gimme a sec to set this up for you.

The binary is called WISE J072003.20-084651.2 (seen by the WISE observatory and named after its coordinates on the sky), or more colloquially "Scholz's stars," since it was first identified by astronomer Ralf-Dieter Scholz. The two objects in the system are a bit odd one is a very low-mass red dwarf star, barely a star at all (it's type M9), and the other really isn't a star but a brown dwarf, an object more massive than a planet but lacking the mass needed to ignite sustained nuclear fusion in its core (which is what makes a star a star).

The low masses of these objects make them very faint, which is why they weren't discovered until 2014. Even worse, they're located in the constellation Gemini, which is in the plane of the Milky Way, where a bazillion stars crowd together, making it harder to spot faint objects.

The faint binary star system WISE J072003.20-084651.2, aka Scholz’s stars, is about 22 light years away, and escaped detection until 2014. Maybe you can see why — and this image is in the infrared where the stars shine more brightly than visible light. Credit: Aladin / 2MASS

The binary system of Scholz's stars is about 22 light-years from the Sun… now. But tracing its motion backward in time shows that it passed very close to us 70,000 years ago. Exactly how close is hard to say, but something less than a light-year seems pretty certain.

This close pass by the binary certainly didn't affect the planets or moons in our inner solar system, but it's possible it did affect the denizens of the very outskirts of our local neighborhood: Oort cloud comets.

The Oort cloud is a roughly spherical collection of possibly trillions of iceballs out in the deep dark. Definitions vary, but it starts roughly 400 billion kilometers out from the Sun, 100 times the distance of Neptune, and may extend to more than ten trillion kilometers: About a light-year.

Which is just how close Scholz's stars passed. Hmmm. Could the binary system's gravity have affected any comets, changing their stately million-years-long orbits, and dropped them down toward the Sun?

Possibly! A team of astronomers looked at a collection of comets with unusual orbits, what we call hyperbolic orbits. Objects on these kinds of paths are moving too quickly to be bound by the Sun as they pull away from the Sun they slow, but they're moving so rapidly the Sun's gravity can't slow them to a stop and reverse their courses. They'll leave the solar system entirely.

There are a few ways comets can become hyperbolic. One is to pass to close to Jupiter or Neptune. If they do, the gravity of these planets can give them a kick in the tail (haha! Ha! Because they're comets!), boosting their velocity just enough to become hyperbolic. We've seen this happen a few times with comets.

Another is a close pass by a star, like Scholz's binary. But how can you tell?

What the astronomers did was look at 339 hyperbolic comets to figure out the shapes of their orbits as carefully as possible, and then traced the motions of these comets backward in time about 100,000 years. This can be done using sophisticated computer models that use the physics of gravitational interactions with the planets, moons, and asteroids to see just how they affect the comets' orbits.

Because the Oort cloud is roughly spherical, you'd expect the comets would come from random directions in the sky. But that's not what they found: There were several clumps in the sky where comets seems to come from more often than other spots. Some of these you expect through random statistics, like flipping a coin and having it come up heads a few times in a row.

You can apply some math to that distribution and determine how much deviation from randomness you expect… And some of the clumps look pretty real. Including one that appears in the sky not too far from the current location of Scholz's stars.

But wait! Not so fast! It's not that clear this means what you think it means. That's the location of Scholz's binary now, but 70,000 years ago, when it passed us, it was in a different part of the sky. I'd expect the comets to be coming from there, not the direction where the binary star is now.

I asked the lead author of the work, Carlos de la Fuente Marcos, about this, and he agreed. The problem is that the position of the binary star system is hard to extrapolate backward accurately, and the farther back you go the more uncertain it gets. You get what I think of as a "probability blob," a biggish area on the sky where the stars probably were, but you can't say for certain where in that area they were.

So the directions those comets came from overlaps with where the stars may have been 70,000 years ago, but it's not certain. And it's certainly not certain enough to rule out the possibility that there may be another cause for the comet clumping.

Artwork depicting the red dwarf/brown dwarf binary system called Scholz’s stars, which passed near Earth about 70,000 years ago (the Sun appears as a bright star to the left). Credit: Michael Osadciw/University of Rochester

And that's why the answer to all this is "maybe." It's possible the gravity from the binary system shook up the outer solar system and sent a bunch of comets our way, but it's possible they're unrelated, too.

That's irritating. But there's a way to do better. One is to keep observing Scholz's system, get better measurements of its velocity in space, so that we can trace it backward better. Another way is to keep looking for more comets, and whenever we find one that's hyperbolic we can add it to the list and see where it falls.

Until then, this is a very interesting hypothesis, but by no means certain.

Another thing they mention that's pretty interesting: They found 8 comets out of the 339 that were moving at speeds that indicate they may be interstellar! In general, comets that start in the Oort cloud and get disturbed in some way accelerate as they fall closer to the Sun, but these were moving rapidly enough (about 1.5 kilometers per second faster than the free fall speed) that it's at least possible they came from another star. We can't say for sure, but still pretty neat.

And there's one other thing I want to add: The press release for this news came with an interesting graphic. Given the timing of the passage of Scholz's star, it happened when humans walked the Earth. In fact there were still Neanderthals along with Homo sapiens at that time! The graphic depicts an ancient person of indeterminate species gazing up at and illuminated by a red star in the sky:

Sadly, this graphic is not accurate even at closest approach, Scholz’s Stars were far, far too faint to see without a telescope, which would have to wait 70,000 years to be invented. Credit: José A. Peñas/SINC

There's a problem here though: Even the brighter of the two objects in the binary is so faint and weak that it would've been invisible to the naked eye! And it's not even close it would've been about 1/100th as bright as the faintest star you can see. I know that seems counterintuitive given how close it was, but a red dwarf at that end of the mass scale is truly a dim bulb. It would have to have passed us ten times closer to be seen at all, and even then it would've been very faint (you might suppose we have that drawing wrong, and that's an alien standing on a planet orbiting the red dwarf — but that doesn't work either the Sun would be as bright as Venus, fainter than depicted, and it's the wrong color anyhow).

Ever look at a picture of Saturn (or anything else with rings) and think &ldquoWow, I wonder what those rings are made of?&rdquo Spoiler alert &ndash they&rsquore just very pretty rocks and ices and dusts. How about this one &ndash Ever look up at the Moon (or any other moon) and think &ldquoWow, I wonderContinue reading “earth&rsquos rings?” Continue reading &rarr

I was watching a documentary about the sheer power and destruction that Mount Vesuvius lay upon those heedless Roman citizens in Pompeii, and it got me thinking about the movement of the tectonic plates. What needs to happen underneath the land to create enough power to bury a city in 15 feet of rubble andContinue reading “Mount Vesuvius and the Pompeiian Disaster: How it happened” Continue reading &rarr

## Fall 2015 - The Symbiotic Binary AG Pegasi

A Once in a Century Opportunity!!

AG Pegasi​ is a very dynamic system. Its last outburst was in 1860-1870 when it went from magnitude V=6, at its brightest, and has been gradually dimming since to magnitude V=9. That is until this year, between May 27t​h​ and June 13t​h​, when this system started brightening again. In the past year the system has brightened by a factor of 6! ​Little is truly known​ about this fascinating target&rsquos outburst phase.

Not much new has been learned since Kenyon et al. wrote about it in 1993. AG Peg is what is known as a symbiotic binary star, first classified as such by Cecilia Payne-Gaposchkin (at Harvard!) in 1957. AG Peg is a ​M III giant​ with a ​hot, compact companion​ star embedded in an ionized nebula with expanding shells of gas. The system is in a ​812 day orbit​.

Photometric monitoring allowed early astronomers to discover a lot about this system. During the previous outburst, the technology did not exist to do really precise photometry and the time coverage was sparse, so there is still a lot of information about the system to be learned.

Another particularly interesting opportunity is to track the changes in the spectra to get a physical understanding of how the system is changing during an outburst. Getting​ photometric​ and ​spectroscopic​ data frequently is very important to our understanding of this unique transient system.

Spring 2015 - Comet Lovejoy

We observed Comet Lovejoy throughout the spring semester after it made its closest approach in January 2015. The above image in BVR shows the bright green comet and the trailing stars as the comet moves through the sky. The green color is from a florescence of diatomic C2 gas.

A chance discovery on January 21, 2014 by Steve Fossey et al. of University College London during an undergraduate telescope training session revealed the closest Type Ia supernova in the past 42 years. Type Ia supernova are valuable distance measures and an explosion this close allows for accurate calibration. The Harvard Observing Project monitored this closely for 4 months in BVRi filters and an Harvard undergraduate Missy McIntosh presented a poster (see below) at the American Astronomical Society meeting in Boston, MA (June 2014).

Fall 2013 and Fall 2014 - TargetAsteroids!

Tracking Asteroid 2005YU55.

We will be participating in the Target Asteroids! citizen science program, which is part of the OSIRIS-REx mission. In 2016, the spacecraft will journey to a Near Earth Asteroid that makes a close pass by Earth every six years and will return a sample of asteroid material. In the mean time, amateur observers - including us - are joining forces to gather more information on NEOs of particular interest to the mission.

Near Earth Objects (or NEOs) are asteroids or comets that are on orbits that take them close to Earth's. Our goal is to do astrometry (measuring position) and photometry (measuring brightness). Astrometry allows us to determine the object's orbit - in particular, you might want to know if it will hit Earth! From photometry, we can measure the rotation period of an asteroid and maybe learn something about it's shape (see, for example, this blog post). Another reason you might be interested in the nearest asteroids is that Planetary Resources announced in Spring 2012 that they are going to mine asteroids.

As an example of what we hope to see, the video to above-left shows Asteroid 2005YU55 on its close approach to Earth in 2011. This video is a composite of 6 images taken by the Fall 2011 SPU21 class.

Fall 2012 - Eclipsing Binary Stars

Eclisping binaries are two orbiting stars which periodically pass in front of each other. Eclipsing binaries are useful because the eclipses tell us about the radii and temperatures of the two stars (with other observations, their masses may also be determined). Most stars are in fact part of binary systems. Some binaries consist of two mid-life stars that are still on the main sequence, some contain one star at a later stage of its evolution, and some contain rarer specimens such as white dwarfs or neutron stars.

With our observations, we'll be helping out the eclipsing binary research being led by the KELT and Kepler teams.

Fall 2011 - PAWM: White Dwarf Monitoring

Data from one of our PAWM teams. Orange cross-hairs show our data. Red circles are the data averaged over short time intervals.

Harvard joined amateur astronomers around the world in the Pro-Am White Dwarf Monitoring (PAWM) Project. During this month-long pilot project, we looked for transits of Earth-sized planets around white dwarfs.

A transit occurs when a planet passes between us an its host star, temporarily blocking some of the star's light. We see the star decrease in brightness and can use this decrease to determine the planet's orbital period and radius. White dwarfs aren't much bigger than Earth itself, so the transit of an Earth-sized planet could block a lot of light.

PAWM observed 46 white dwarfs, none of which showed evidence for an Earth-sized planet. However, one white dwarf was seen to vary sinusoidally.