Millions of overlooked galaxies
When researchers took a closer look at surveys of galaxies in the local universe, they found many had been mischaracterised. More careful analysis of images revealed that 21 galaxies that originally looked like big 3D clouds of stars – “giant elliptical galaxies” – were actually flat 2D disc galaxies with bulges in the middle.
Those bulges have “exactly the same physical mass and compact size as the galaxies in the early universe,” Graham says. This suggests that the vast majority of compact spheroids that were thought to have disappeared aren’t actually missing – they’ve just grown a disc, possibly by gathering hydrogen gas and stars from smaller galaxies but without major mergers.
The results suggest that there are 1000 times more of these galaxies in the local universe than previously thought – roughly as many as there were in the early universe.
It has been widely remarked that compact, massive, elliptical-like galaxies are abundant at high redshifts but exceedingly rare in the universe today, implying significant evolution such that their sizes at z ~ 2 ± 0.6 have increased by factors of 3 to 6 to become today’s massive elliptical galaxies. These claims have been based on studies that measured the half-light radii of galaxies as though they are all single-component systems. Here we identify 21 spheroidal stellar systems within 90 Mpc. This abundance of compact, massive spheroids in our own backyard had been overlooked because they are encased in stellar disks that usually result in galaxy sizes notably larger than 2 kpc. Moreover, this number density is a lower limit because it has not come from a volume-limited sample. The actual density may be closer to 10^−4, although further work is required to confirm this. We therefore conclude that not all massive “spheroids” have undergone dramatic structural and size evolution since z ~ 2 ± 0.6. Given that the bulges of local early-type disk galaxies are known to consist of predominantly old stars that existed at z ~ 2, it seems likely that some of the observed high-redshift spheroids did not increase in size by building (three-dimensional) triaxial envelopes as commonly advocated, and that the growth of (two-dimensional) disks has also been important over the past 9–11 billion years.
2. As many as half of all stars in the universe lie in the vast gulfs of space between galaxies, an unexpected discovery made in a new study using NASA rockets. These stars could help solve mysteries regarding missing light and particles that theory had suggested should exist, scientists say. The stars were ejected from their birthplaces by galaxy collisions or mergers.
The EBL is essentially all the accumulated light from stars over the history of the universe and ranges in wavelength from the ultraviolet, through the optical, and to the infrared. To get a good look at it, Bock, Cooray, and an international team of colleagues built a detector, called the Cosmic Infrared Background ExpeRiment (CIBER), that could be launched to the edge of space on a rocket and collect images with two 11-centimeter telescopes.
The EBL has long been mysterious to scientists. Observing it from Earth is hard because so many other, local sources of light must be stripped away before it is possible to see the light from further back in the universe’s history. And when astronomers have managed to get a look at the EBL, usually using orbiting infrared telescopes such as Hubble and Spitzer, the ups and downs—or fluctuations—of its light do not appear to coincide with known light sources. About 10 years ago, a team from Goddard Space Flight Center in Greenbelt, Maryland, used the Spitzer telescope to study the EBL and concluded that the fluctuations of light must be produced by primordial galaxies and black holes in the very early history of the universe, says team member Samuel Moseley.
The researchers also looked at the total brightness of the EBL and found that it was in the same ballpark as that from all the known sources—stars and galaxies—at that wavelength. That suggests that there may be as many stars outside galaxies as there are inside.
3. Our galaxy could be teeming with “homeless” planets, wandering the cosmos far from the solar systems of their birth, astronomers have found. The study could help clear up a long-running debate of whether free-floating planets really exist, and how common they are.
“The results are convincing enough that I suspect this paper will be cited for years to come as the best evidence of free-floating planets,” says Dimitri Veras, an astrophysicist at the University of Cambridge in the United Kingdom, who was not involved with the study.
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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