Buzz
The universe is filled with unsolved mysteries. From the questions about stars that remain unanswered to the distant planets and moons within our solar system, there's much to uncover using our telescopes. But some puzzles go beyond our solar system, and the ones listed here are truly galactic in scale.
10. The Sun's Birthplace
Stars like our sun are formed in clusters alongside other similar stars, originating from the same gas cloud and sharing the same chemical makeup. However, after studying 100,000 stars within 325 light-years from Earth, only two come close to resembling the Sun. This suggests that our sun is unique, having either been ejected from or drifted away from its original cluster around 4.5 billion years ago.
One potential birthplace for the Sun was Messier 67, a star cluster in the Cancer constellation about 2,900 light-years from Earth. The stars in this cluster share similar age, temperature, and chemical composition to our Sun. However, a 2012 study by astrophysicists from the National Autonomous University of Mexico showed that M67 doesn’t match.
For the Sun to have been expelled from M67, an unlikely alignment of several massive stars would have been needed. The speed required to eject it would have torn apart the planetary disk, preventing Earth from ever forming. Additionally, the vertical motion of M67 in the galactic plane is five times greater than that of the Sun, which should have been consistent.
It’s possible that the Sun’s original cluster no longer exists, with all its sibling stars drifting apart over time. Another theory is that the Sun originated closer to the center of the galaxy, where many stars similar to it are located.
The European Gaia satellite, launched in 2013, offers the best opportunity to determine the Sun’s origin. Gaia is mapping the chemical makeup of one billion stars, with its mission concluding by 2018, offering unmatched insight into the galaxy’s evolution.
9. Starry Waves
Astronomical discoveries are often not made by simply peering through a telescope and observing the immediate surroundings. In many cases, an observatory gathers a wealth of data from a section of the sky, and scientists take years to interpret the information. One such initiative is the Sloan Digital Sky Survey. Using a telescope in New Mexico, it has spent the past decade studying 930,000 galaxies, 120,000 quasars, and almost half a million stars in the Milky Way.
With this extensive data, a group of astronomers observed an interesting pattern in the vertical distribution of stars. These stars tend to cluster together, and upon examining 300,000 of them, the team discovered a pattern resembling a sound wave. They termed this phenomenon “cosmoseismology” in their paper, proposing that something had caused the galaxy to 'ring like a bell.'
The most plausible explanation is that an object collided with and passed through our galaxy within the last 100 million years. While the researchers couldn’t identify the exact object, it may have been a dwarf galaxy or potentially a structure made of dark matter. It's possible that multiple events were involved, and the wave may even be the result of a continuous occurrence.
Once again, the researchers are hopeful that the billion stars mapped by Gaia will provide crucial insights. They suspect that a hidden 'rich pattern of wave structures' may exist throughout the galaxy, which could offer an entirely new perspective on its history.
8. High-Velocity Clouds
High-velocity clouds (HVCs) were first discovered in 1963. These clouds of interstellar gas travel at speeds and in directions that differ from the Milky Way’s rotation, moving at least 50 kilometers (32 miles) per second faster. Mostly composed of hydrogen, they are thought to be falling into our galaxy from intergalactic space. However, their origin remains a mystery.
Jan Oort, one of the researchers who identified these clouds, proposed that the gas might be a remnant from the galaxy’s formation. Another theory suggests that the gas is part of a Galactic Fountain, ejected from the Milky Way and now falling back in. If this is true, the rising gas would be difficult to detect due to the obstructing material around it.
The gas might also originate from objects in orbit around the Milky Way. One such object is Complex H, a small galaxy believed to be in a retrograde orbit around our own. As it moves, it releases gas into the Milky Way.
One HVC, Smith’s Cloud, is heading toward the Milky Way’s disk at a speed of about 73 kilometers (45 miles) per second and is expected to merge with our galaxy in roughly 27 million years. Its path indicates that it already passed through the Milky Way about 70 million years ago. This should have torn the cloud apart, and scientists speculate that a halo of dark matter may have helped keep it intact.
7. Magellanic Clouds
The Magellanic Clouds are neighboring galaxies to the Milky Way, first discovered during Ferdinand Magellan’s groundbreaking voyage around the world in the 16th century. The Large Magellanic Cloud spans 14,000 light-years and is located around 160,000 light-years from Earth. The Small Magellanic Cloud, half the size of the Large Cloud, is situated 30,000 light-years further away. By comparison, the Milky Way is 140,000 light-years across.
The Magellanic Clouds are approximately 13 billion years old and were once thought to be orbiting the Milky Way. However, Hubble measurements now indicate they are traveling twice as fast as initially believed. If this is true, the Milky Way may not have enough mass to hold them in orbit. Determining whether they are in orbit has become a fresh puzzle, and if they are, it would suggest that the Milky Way’s mass is double what we previously thought.
The Magellanic Clouds, whether they are permanent or just passing through, continue to captivate researchers. Recently, scientists have resolved a mystery that has puzzled them for forty years concerning the origin of the Magellanic Stream, a vast trail of gas that wraps around half of the Milky Way. It was found that most of the gas originates from the smaller cloud, although the oxygen and sulfur levels in newer areas of the stream resemble those in the larger cloud.
In 2007, Australia’s Parkes telescope detected a burst of radio waves while observing the smaller cloud. The intense power of the burst suggests an extraordinary event, possibly a collision between neutron stars or the demise of a black hole. While it is almost certainly from a source located farther away than the cloud itself, the precise origin remains an unresolved mystery.
6. Galaxy X
One of the most famous astronomical conspiracy theories revolves around the concept of "Planet X." This theory posits that a planet, as large as Jupiter, follows an erratic orbit around the Sun, secretly monitored by NASA. While this idea is filled with problems, there is a genuine possibility for the existence of "Galaxy X." This is a dwarf galaxy located on the opposite side of the Milky Way, hidden from our view by interstellar gas and dust. Galaxy X could contain up to 85 percent dark matter.
The search for Galaxy X is being led by UC Berkeley theoretical astronomer Sukanya Chakrabarti. She has devised a technique to identify dark galaxies by studying the ripples caused by these galaxies in the distribution of hydrogen gas within spiral galaxies. Hydrogen gas extends up to five times further than the star-filled regions, and the gravitational pull of orbiting galaxies creates detectable ripples in this gas.
Chakrabarti estimates that Galaxy X’s mass will be about one-hundredth of that of the Milky Way. Her method to uncover these hidden galaxies has been tested on other galaxies with known companions and can detect objects as small as one-tenth of that size.
5. The Lithium Problem
The lithium problem has been a persistent issue in cosmology. As the third-lightest element in the universe, after hydrogen and helium, lithium's expected levels are predicted by Big Bang models. These predictions work for every element except lithium.
In the oldest stars of the Milky Way, lithium-7 is found at roughly one-third of the anticipated levels, while lithium-6 appears in quantities around 1,000 times higher, though it is far more difficult to measure accurately.
No satisfactory explanation has been found. Proposed solutions disrupt the expected ratios of other elements. The challenge has only grown more complex over time. A 2008 astrophysics paper aptly expressed the frustration in its title A Bitter Pill: The Primordial Lithium Problem Worsens.
Research suggesting that the early galaxy may have been populated by microquasars has only added to the confusion. These small black holes eject super-heated plasma with enough energy to fuse hydrogen into helium. In 2012, a team from Sweden and Germany calculated that if just 1 percent of the Milky Way's microquasars generated lithium-7, they would produce an amount similar to that predicted by the Big Bang. Essentially, microquasars have made the lithium problem even more difficult to solve.
A recent hypothesis suggests the existence of axions, hypothetical particles associated with dark matter, to explain the issue. Predictions regarding lithium-7 levels rely on the amount of light present in the early universe, calculated using the cosmic microwave background that emerged about 380,000 years after the Big Bang. It's believed that axions could have cooled the photons during this time, leading to an underestimation of light levels and, consequently, an overestimation of lithium-7.
However, this theory is far from conclusive, as it would imply that there are twice as many neutrinos as we currently observe. Moreover, axions are not even the leading candidate to explain dark matter, and their existence remains highly uncertain.
4. Galactic Warp
In numerous galaxies, the gas and dust found between stars is concentrated into a thin layer, and our Milky Way is no exception. The term 'thin' is relative—this disk measures about 240 light-years in thickness at its thinnest, though this is just a tiny fraction of the galaxy's overall width. Our solar system is embedded deep within this layer, which is primarily composed of atomic hydrogen and helium.
While some galaxies feature flat disks, many show bends and curves, a phenomenon known as galactic warp. Some of these warps resemble the integral sign from calculus or a stretched 'S' shape. Others form U-like shapes, and a few are completely asymmetrical. Multiple factors could be responsible for these warps, and it seems that an ongoing process is at play, as models indicate that warps would naturally flatten over time if galaxies simply formed that way.
In the case of the Milky Way, our disk appears flat when viewed from our position in the galactic plane. It curves north in one direction, then dips downward before curving back up at the far end. The overall shape is reminiscent of a wave.
Researchers from UC Berkeley were able to describe the galactic warp as a combination of three distinct vibrations within the disk. The first involves a flapping at the edges, paired with a sinusoidal wave resembling the skin of a drum, and a saddle-shaped oscillation. Together, these vibrations contribute to a sound that's 64 octaves below middle C.
The most plausible explanation for the galactic warp is that it results from the Magellanic Clouds moving through the dark matter halo surrounding the Milky Way. Initially, it was believed that the clouds didn’t have enough mass to cause a warp. However, researchers propose that as the clouds pass through the halo, they create vibrations similar to a ship's wake, which resonates through the galaxy and causes the disk to warp.
3. Willman 1
In 2004, a group of astronomers from New York University made an intriguing discovery while analyzing data from the Sloan Digital Sky Survey. They were searching for faint companion galaxies to the Milky Way, but what they uncovered didn’t quite fit the traditional definition of a galaxy. In fact, this group of stars didn’t conform to any conventional category.
This object was designated SDSSJ1049+5103, or Willman 1 for short. It orbits approximately 120,000 light-years away from the Milky Way. It might be a dwarf galaxy, or perhaps a globular cluster, but both possibilities come with complications. Globular clusters typically contain several hundred thousand stars, whereas Willman 1 contains fewer than a thousand. Some have suggested it could be a cluster from a smaller galaxy, with one physicist likening it to 'a tiny mite riding in on a flea as it, in turn, latches onto a massive dog.'
If Willman 1 is indeed a galaxy and not a cluster, it could challenge another prevailing theory. Computer models of the Milky Way's formation suggest there should be hundreds of smaller galaxies nearby, yet only 20 have been discovered. One possible explanation is that galaxies with a mass less than 10 million suns are too faint to produce many stars, making them nearly invisible.
Further investigation of Willman 1 reveals that its mass is only about half a million suns, significantly below the expected threshold. It’s possible that undetected dark matter could be present in Willman 1, or it may have lost some of its mass over time. Either way, it remains a collection of stars that raises more questions than it provides answers.
2. Hypervelocity Stars
Most stars orbit the galactic center at a speed similar to our sun’s, around 230 kilometers (143 miles) per second. However, some stars, about one in every billion, travel three times faster than that. These stars are known as hypervelocity stars. The first such star was discovered by astronomers from the Harvard-Smithsonian Center for Astrophysics in 2005, and since then, dozens more have been identified.
What makes hypervelocity stars so intriguing is their speed: they’re moving fast enough to potentially break free from the galaxy’s gravitational pull. The mystery lies in the source of this incredible velocity.
HE 0437-5439, one of the fastest stars discovered, is thought to have a tumultuous history. The prevailing theory suggests that a triple-star system ventured through the galactic center, where the central black hole tore one star away. This caused the remaining two stars to be ejected, eventually merging into a blazing blue giant that now speeds out of the Milky Way at 2.5 million kilometers (1.6 million miles) per hour.
LAMOST-HVS1, the closest hypervelocity star to Earth, may have been propelled out of the galaxy due to an interaction with the central black hole. However, it might have originated from the galaxy's disk, which suggests the presence of a middleweight black hole in our galaxy. These are black holes of an intermediate size, falling between stellar-mass and supermassive black holes. To date, only one such black hole has been observed, and it lies outside our galaxy.
1. Diffuse Interstellar Bands
Since its discovery in the 19th century, spectroscopy has been a fundamental tool in astronomy. It involves analyzing the wavelengths of radiation from objects in space to determine their composition, among other properties. Each atom and molecule absorbs unique wavelengths of light. By examining the light patterns that reach us, we can deduce what those objects have interacted with along the way.
In 1922, astronomer Mary Lea Heger detected spectral bands that defied explanation. Scientists initially concluded these bands must be caused by something in interstellar space, but the exact nature of the source remained a mystery.
Hundreds of these spectral bands have since been identified across infrared, ultraviolet, and visible light spectrums. This phenomenon became known as the 'classic spectroscopic problem' of the 20th century. Speculations ran rampant in scientific literature, proposing all possible types of matter as potential causes. Today, large carbon-based molecules are considered the most probable culprits, possibly accounting for up to 10 percent of the galaxy's carbon content.
In 2011, diffuse interstellar bands were detected for the first time in the direction of the Milky Way’s center. This discovery offers a significant clue: it suggests that these molecules can endure the extreme conditions found at the heart of our galaxy. The newly observed bands also extend further into the infrared spectrum than any found before.
Thomas Geballe, an astronomer based in Hawaii, hopes that these new observations will bring scientists closer to solving the mystery. He speculates that the molecules responsible for these bands may hold clues about the origins of life, possibly coming from complex chemicals that played a role in seeding life on Earth.
