Cosmic Neighbors Inhibit Star Formation, Even in the Early-Universe

W. M. Keck Observatory press release

Galaxy cluster MACS J0416
Massive galaxy cluster MACS J0416 seen in X-rays (blue), visible light (red, green, and blue), and radio light (pink). Credit: NASA, CXC, SAO, G.Ogrean, STSCI, NRAO, AUI, NSF
The international University of California, Riverside-led SpARCS collaboration has discovered four of the most distant clusters of galaxies ever found, as they appeared when the Universe was only four billion years old. Clusters are rare regions of the Universe consisting of hundreds of galaxies containing trillions of stars, as well as hot gas and mysterious Dark Matter. Spectroscopic observations from the W. M. Keck Observatory on Maunakea, Hawaii and the Very Large Telescope in Chile confirmed the four candidates to be massive clusters. This sample is now providing the best measurement yet of when and how fast galaxy clusters stop forming stars in the early Universe.

“We looked at how the properties of galaxies in these clusters differed from galaxies found in more typical environments with fewer close neighbors,” said lead author Julie Nantais, an assistant professor at the Andres Bello University in Chile. “It has long been known that when a galaxy falls into a cluster, interactions with other cluster galaxies and with hot gas accelerate the shut off of its star formation relative to that of a similar galaxy in the field, in a process known as environmental quenching. The SpARCS team have developed new techniques using Spitzer Space Telescope infrared observations to identify hundreds of previously-undiscovered clusters of galaxies in the distant Universe.”

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Getting to the Lava (Revised)

The 61G flow reached the ocean a month ago, but only this last weekend did I get a chance to go out and see it for myself. It is quite a bit further to go than previous visits, about four and a half miles, but is it also much easier. I realized that my Getting to the Lava post is a bit outdated and a serious update is in order.

The 61G lava flow ocean entry at Kamokuna
The 61G lava flow ocean entry at Kamokuna
The 61G flow began on May 24th, breaking out on the southeastern flank of Pu’u O’o. The flow moved fairly quickly, cutting the re-built Chain of Craters Road and entering the ocean on July 26th. The flow is quite vigorous with an ample supply of lava. There are currently multiple surface breakouts and multiple ocean entry points. The flow is building new land near Kamokuna, the lava delta has added around 11 acres to the Big Island in one month.

61G Lava Flow Map
Map of the 61G lava flow as of July 2nd
With easier access and a dramatic ocean entry the 61G flow is drawing large crowds of visitors that have come to see the spectacle. In my opinion the trip is very much worth the effort. Still, there are inherent risks in experiencing raw nature like this. A little preparation is in order and may prevent a visit from becoming an emergency.

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One of the most striking features of Mauna Kea is the māmane forest. These native trees are generally found from 5,000-9,000ft elevation on the slopes of the mountain. The māmane (Sophora chrysophylla) is highly variable in appearance, growing as a shrub or a tree, bearing bright yellow flowers in late winter months.

At around 8,000ft there is a fence built to keep feral sheep and cattle out of the māmane forest and to protect the endangered palila (Loxioides bailleui).  Above this fence the trees thrive, below the fence the forest is nearly dead.  The hillsides scattered with relic trees where no young trees survive the herbivores to replace them. While desolate in appearance these old trees can be quite photogenic.

Perseid Meteor Shower

Over the next few days the Perseid meteor shower will peak. As the most reliable shower each year this is also the most viewed meteor shower. Plentiful shooting stars combined with warm summer evenings makes this shower the easiest and most comfortable to view across much of the northern hemisphere.

The comfort of summer meteor observing marks quite a difference from the other reliable showers such as the Leonids and Quadrantids, that occur in November and January. Consider a warm summer night under a dark sky full of stars, a picnic blanket, relaxing while shooting stars streak across the sky. What could be better?

Leonids in Orion
A pair of Leonid meteors streak through Orion
The Perseid meteor shower occurs when the Earth passes through a stream of debris along the orbit of Comet Swift-Tuttle. This shower has been consistent throughout recorded history, mentioned in Chinese, Japanese and Korean records as early as the 1st century.

Active from July 17th to August 24th, the shower will build slowly for weeks before the peak. A week before or after peak the shower can still be seen with around 20 meteors each hour. With a radiant high in the constellation of Perseus this is a northern hemisphere shower, for southern observers the radiant never rises above the horizon.

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